Chapter 10 Abiotic filtration methods for live coral systems in public aquaria

18 Pages·2008·0.64 MB·English

Advances in Coral Husbandry in Public Aquariums. Public Aquarium Husbandry Series, vol. 2. R.J. Leewis and M. Janse (eds.), pp. 85-102
© 2008 Burgers’ Zoo, Arnhem, the Netherlands.
Chapter 10
Abiotic filtration methods for live coral systems
in public aquaria
RichaRd TeRRell, JR.1, RichaRd KlobuchaR, JR.2 and caRRie PRaTT3
1 Pittsburgh Zoo & PPG Aquarium, One Wild Place, Pittsburgh, PA 15206, USA
[email protected]
2 University of Hawaii - Waikiki Aquarium, 2777 Kalakaua Avenue, Honolulu,
HI 96815, USA
[email protected]
3 Columbus Zoo and Aquarium, 9990 Riverside Drive, Powell, Ohio 43065, USA
[email protected]
AbstrACt
Over recent decades, advances in life support systems (LSS) for captive corals have
increased public aquariums’ ability to more closely mimic water quality conditions
found on coral reefs. This, in turn, has allowed these institutions to keep, exhibit and
reproduce an increasing diversity of coral species. We will discuss abiotic LSS in terms
of mechanical and chemical filtration. Mechanical filtration will focus on such methods
as filter floss, cartridge filters, rapid sand filters and bag filters. Examples of chemical
filtration included are ozone, ultraviolet sterilizers, carbon and other adsorptive media
and ion exchange resins. Perhaps the most significant development in abiotic LSS for
living reef systems is the use of foam fractionation. This unique life support element
functions as both chemical and mechanical filtration. We will discuss the advantages,
disadvantages and caveats of each filtration device or medium as they relate to the
husbandry of live corals in public aquaria. The authors also conducted a survey of public
aquaria that exhibit live corals to ascertain the prevalence of different abiotic life support
components in the industry. Foam fractionation was used in all but one of the responding
institutions. The second most prevalent filtration device was activated carbon, with well
over half the respondents using it either intermittently or continuously.
IntroduCtIon
The success of keeping live corals in public conducted a brief survey (see Appendix 1)
aquaria has advanced significantly in recent of public aquaria throughout the world to
decades. Much of this can be directly related determine which abiotic filtration devices were
to improvements in filtration methods and an in use in public institutions at this time. The
increased understanding of the interactions results of this survey are summarized in Table
between water quality and captive coral health. 1. We will further limit our discussion to those
In this chapter we will summarize the function, devices used in public aquaria as determined
advantages, disadvantages and caveats by this survey.
associated with the different filtration methods
employed by public aquariums in caring for
live corals.Filtration can generally be broken MeChAnICAl FIltrAtIon
into three functionalities: mechanical, chemical
and biological (Moe, 1989). While some Mechanical filtration is defined by Spotte (1970)
biological filtration devices perform mechanical as “the physical separation and concentration
or chemical filtration functions as part of their of suspended particulate matter from circulating
normal functionality, in this paper we will water. It is accomplished by passing the water
focus on non-living, or abiotic, mechanical through suitable substrata or septa that trap
and chemical filtration devices. The authors the particles.” Its functions in a closed marine
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aquarium are to: 1) reduce turbidity caused by or “cartridge” filters, undergravel or sub-sand
microorganisms and other particulate matter, filters, diatomaceous earth filters and settling
2) lower the level of organic colloids and 3) sumps. As with any life support component, the
remove accumulated detritus from the system choice of which mechanical filtration methods
(Spotte, 1970). Reduced turbidity allows better to utilize is determined by the individual
viewing of the exhibit animals by the public. preference of the designer and operator as well
It also improves light penetration, which can as the application and the filtration goals. We
be important for photosynthetic corals and will briefly describe the function, advantages
tridacnid clams. Removing detritus from the and disadvantages of each filtration method.
system helps to keep nutrient levels low by
removing the detritus before it decomposes Rapid sand filters
into nitrates, phosphates and other nutrients Rapid sand filters, or high rate sand filters,
which can fuel algal growth. remove particles by passing water through
a bed (mixed or uniform) of sand or a similar
Most mechanical filters require attention from medium. Cleaning is accomplished by reversing
the aquarist to remove the trapped material the flow of water through the sand bed and
from the filter media (thereby removing detritus sending the water to waste (backwashing).
from the system). Oxidation-reduction potential Sand filters’ efficacy is effected by the size,
(ORP) is measured in mV and is the sum of shape and grading (variation in size) of the
all reactions, or half-reactions, involving the sand grains, as well as accumulation of detritus
transfer of electrons (www5). Regular cleaning in the sand bed. Smaller sized, more angular
of a mechanical filter can also help maintain sand grains will yield a higher particle trapping
higher oxidation-reduction potential (ORP) efficiency but will require a shorter time interval
in the system (Paletta, 1989), allowing the between backwashes (cycle time). While
aquarist to achieve and maintain an ORP in the detrital accumulation increases undergravel
ideal range of 300-380 mV (www5). Increased filters’ efficacy significantly, its effect is less
ORP can help to prevent or control microalgal pronounced on rapid sand filters.
growth in a system (Paletta, 1988). So properly
maintained mechanical filters not only improve In a reef system, the advantages of rapid sand
water clarity, but they can also be a great aid filters are 1) their relative ease of cleaning,
in preventing and controlling nuisance algae in 2) high flow rates and 3) high efficiency at
reef aquaria. removing particulate matter. If tank water is
Many modern reef aquarists do not continuously used to backwash the sand filter this affords
employ dedicated mechanical filters; relying the system a partial water exchange. But if the
instead on foam fractionators, direct siphoning water is not “recovered” for use in a non-coral
of settled material during partial water changes, system, the waste of salt can be a significant
or on live detritivores and bacteria in the system expense. Backwashing with freshwater has
to remove or consume detritus. Arguments the advantages of eliminating salt waste and
against the use of any mechanical filtration in of limiting marine bacterial growth in the filter.
reef systems include: 1) removal of potential If freshwater is not used to backwash the sand
coral food (in the form of plankton, bacteria, filter, marine bacteria can colonize the sand.
and suspended organic material) from the This can be problematic in that it provides a
system, 2) trapping of detritus in the systems high-flow area in which detritus accumulates
where it can decompose and elevate dissolved and can be quickly broken down by the bacteria
nutrient levels and 3) it is unnecessary because into algal nutrients.
foam fractionation can remove particulates Sand filters are also used in concert with
when properly applied and maintained. Foam lanthanum chloride or ferric chloride to aide
fractionators will be addressed separately in phosphate export. When the lanthanum
within this Chapter. chloride or ferric chloride is added to the system,
it bonds with dissolved phosphate to produce
Mechanical filters can be employed intermittently a flocculent that accumulates in the sand
or continuously depending on the preference filters and is backwashed out of the system.
of the aquarist and the type of filtration in use. Diatomaceous earth powder (see section on
There is a wide range of devices in use including diatomaceous earth filters) can also be added
rapid sand filters, filter bags (in a gravity or to a sand filter to polish the water. But this will
pressure configuration), filter floss, “pleated” cause the sand bed to clog rapidly. So it should
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be followed shortly by a backwash. been used on live coral systems as well. One
institution removed it from their system as a
Sand filters are used more commonly on large precaution when they read that AFM removes
(>15,000 L) live reef exhibits than smaller heavy metals (Janse, pers. com.).
exhibits. This is largely a function of the volume
of particulates in such a system, versus a Possible disadvantages
smaller reef system. But the flow required to AFM is very expensive, when compared to
operate a rapid sand filter is also a possible silica sand (as much as five times the cost).
explanation. Smaller systems may not require, But its advantages often allow an institution
or be able to tolerate, high enough flow rates to to recover the additional costs in as little as
allow proper function of a rapid sand filter. sixteen months (McEwan, EUAC jaar opzoekn).
This medium requires further research and
Activated Filtration MediaTM (Dryden Aqua, testing before it can be viewed as a safe and
Ltd., Edinbugh, Scotland) effective option for use on closed system live
Activated Filtration Media, or AFM, is an coral exhibits. Potential research topics could
alternative media for sand filters. It is an include: trace metal removal by AFM in closed
activated form of glass. The manufacturer system aquaria, potential for erosion and
claims that its benefits include: release of medium into the exhibit system,
long-term effects of AFM on live coral water
1) “Increases water clarity by removal of quality parameters, and relative growth of coral
colloidal matter in systems using AFM (compared to traditional
2) Remove at least 50% more solids from sand filter sand).
the water, including bacteria, algae and
protozoa Filter floss and gravity-fed filter bags
3) Reduce the amount of nitrate produce by Polyester filter floss and polypropylene
reducing the mineralization of protein bags are often used between an overflow
4) High surface negative zeta potential or surface skimmer and a pump or sump to
attract +ve charges organic molecules trap particulates. Efficacy will be influenced
5) High surface oxidation potential, helps by the pore size of the material and detrital
to crack organics, just like ozone and accumulation. In general, finer pore size
UV-C systems material costs more than coarser material.
6) Use only ½ the amount of back-wash Because they are in line from the surface
water skimmer to the pump or a sump, these filter
7) Removes colour by catalytically media do not put back-pressure on pumps like
cracking organic molecules, due to a rapid sand filter, cartridge filter or pressurized
surface oxidation potential bag filter can. They are relatively easy to add to
8) Adsorbs micron and sub-micron or remove from the system. Cleaning to remove
particles including organic molecules the trapped debris can be accomplished with a
(and colour), 100 % released on back- hose or in a washing machine. Filter floss does
wash into waste water not generally last through many cleanings.
9) AFM will not generate solids & Depending on the bio-load of the system, both
bacteria, or periodically dump solids & of these media can clog quickly, necessitating
bacteria into the water. Sand filters will cleaning or changing frequently. They are used
periodically discharge into the product both intermittently and continuously in public
water, see report on drinking water aquarium applications.
treatment
10) Will minimise phosphates, especially Settling sumps
when combined with NoPhos due to A settling sump is simply a container, external to
high surface zeta potentia “ (www1) the main aquarium, where water flow is slowed
down, allowing suspended solids to settle on
Tony McEwan reported on use of AFM in the the bottom of the container. If a bulkhead
incoming raw water system at The Scientific and valve are placed low on this sump, the
Center in Kuwait. He saw increased water clarity, accumulated solids can then be drained off to
reduced water color, decreased backwash time, waste. Alternatively, the accumulated debris
lowered ozone usage, and no coagulation of can be manually siphoned out or pumped
the medium (McEwan, EUAC, 2005). AFM has out to waste. This can be an effective means
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of removing solids from the main system. can be good in that the debris can then be
Because the removal of the solids from the removed from the system. But the lack of
sump potentially requires waste of some any bypass within the filter itself means that
system water, it can be costly over time. But clogged media will dramatically reduce flow
this also affords a chance for partial water and put backpressure on the pump if there is
changes. Sumps can also occupy a large no bypass line plumbed into the system. The
footprint if a long or wide and shallow sump high efficiency of these types of filters and the
is used. A tall sump saves footprint space, but resulting tendency to clog quickly means that
makes access to the bottom of the sump more they are more suited to intermittent use (e.g.,
difficult. following a major scrubbing of the rockwork) in
a live coral system with any significant bioload,
Sumps offer a myriad of other advantages unless the aquarist is committed to cleaning
including, but not limited to: 1) a convenient and replacing filters frequently.
place to add other filtration components
(mechanical, chemical, biological, or others), Diatomaceous earth filters
2) holding space for fish from the main system, Diatomaceous earth, or DE, filters are similar
3) a place to add supplements or additives to the cartridge filters in that the filter element
away from the inhabitants of the main tank. All is made up of a supportive core covered by a
of these can be compatible with the use of the fibrous polypropylene or polyester cloth filter
sump as a settling area, provided they do not sleeve. What sets them apart is that the filter
increase water flow in, or through, the sump. sleeve is then coated with a layer of graded
When they are employed on public aquarium skeletal remains of diatoms (DE powder) called
coral tanks, sumps are generally a permanent the filter cake. The filter cake is held in place
and continuous part of the LSS. by vacuum or pressure. It prevents debris from
permanently clogging the filter element and
Cartridge (pleated) filters and pressurized increases the efficiency of the filter element.
bag filters For permanently installed DE filters, it is often
Both pleated filters and pressurized bag filters necessary to install a “precoat pot” to facilitate
consist of a closed cylinder except for the inlet pre-coating the filter element with fresh DE
and outlet pipes. Water is forced through the powder after cleaning. Efficacy of DE filters
cylinder and the appropriate filter medium can be affected by the precoat (the new layer
by the pump. There is usually no bypass of of DE after cleaning the filter element), the
water within the filter such that any water, or surface area of the filter element, and cleaning
debris, entering the filter must pass through the of the filter element (Spotte, 1970). Because
filter media (or be trapped by it). In the case diatom tests are composed primarily of silicate,
of cartridge filters, the medium is usually a extended use of a DE filter could theoretically
pleated polyester fiber cloth over a rigid core elevate silicate levels in the system, causing
cartridge. The same filter bags (or socks) that unsightly blooms of live diatoms.
were discussed earlier function as the medium DE filters are highly efficient, meaning that they
in pressurized bag filters. are very good at removing even very small
In both cases the media is usually rated at a particles in a relatively short time. But this also
given pore size, usually in microns. So efficacy means that they clog very quickly. So they
can be related to this pore size, detrital loading are often used intermittently to “polish” the
and surface area of the filter cartridge or system water to the point that it sparkles, often
bag. Smaller pore sizes are more efficient at immediately after events that cloud the water
removing particles from the system, but they like stirring sand or scrubbing rockwork.
require more frequent cleaning by the aquarist.
Both cartridges and bags can be cleaned with a Undergravel or sub-sand filters
pressure nozzle on a hose and a chlorine bleach Undergravel filters (UGF’s) consist of a
soak. While the filter bags can be machine- perforated plate on the bottom of the tank
washed, the pleated cartridges cannot. Both covered by gravel or sand. Water is moved
types of media have a limited useful life and through the gravel where detritus is trapped
must eventually be replaced. in two ways: 1) physically in the interstices of
the gravel bed and 2) electrostatically to the
In heavy load situations, these filters’ efficacy gravel surface (Spotte, 1970). Normal water
means that they will clog very quickly. This flow for a UGF filter is down through the gravel,
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through the perforated plate and up a lift tube organic acids, and many others may effect
back to the main tank. growth, disease resistance, and the metabolic
stress rates of our animals (Delbeek and
In “reverse flow undergravel filters” the water Sprung, 2005). When used properly with
is pumped down under the plate and flows other forms of mechanical and biological
up through the gravel. If this water is pre- filtration, which serve to remove or break down
filtered mechanically in some way before being particulate organic compounds (POC), chemical
pumped under the filter plate, it leaves little filtration can combat the negative effects of
detritus under the gravel bed (avoiding this DOC on system inhabitants by removing them
disadvantage of normal flow UGF’s) and helps before they accumulate; thereby reducing the
to avoid detritus from settling in the substrate. If concentrations of total organic compounds
raw tank water is pumped under the filter plate, (TOC), lightening filter loads, reducing nitrate
it can deposit large amounts of detritus there, levels, and increasing water clarity by removing
where it is difficult for the aquarist to remove it the organic compounds responsible for the
from the system. yellowing of system water.
A perceived disadvantage of normal and As mentioned earlier, three processes make
reverse-flow UGF’s is that they act as a biofilter up chemical filtration, and most good chemical
where detritus is efficiently broken down filter media use some aspect of each one to
into nitrate and phosphate, thereby feeding remove as many different dissolved organic
nuisance algae. At the same time, they require compounds or other specific compounds,
the aquarist to siphon clean the substrate to such as toxic heavy metals, as possible. The
remove the trapped detritus. This can remove absorption property of chemical filtration media
large numbers of detritivores from the system draws a fine line between mechanical and
along with the detritus, thereby removing a chemical filtration. Instead of collecting large
biological detritus sink. According to our survey suspended particles from the system water,
(Table 1), these filters are rarely used in today’s media that use absorption collect and “trap”
public aquarium live coral aquaria. tiny individual molecules within the porous,
channeling maze that runs throughout each
bead, fiber, or granule of media. Unfortunately,
CheMICAl FIltrAtIon there are no attractive charges or bonds to
keep these molecules secured in place, and
In order to understand the relevance of these media can “fill” or become exhausted.
chemical filtration in coral, clam, and other When this happens the trapped molecules can
invertebrate applications, it is helpful to have find their way back into the system water.
an understanding of what chemical filtration
is, why it is used, and how it works in the first Media such as ion-exchange resins use the
place. Chemical filtration can be defined as the charge of an ionized molecule to bond to their
removal of compounds from a solution through oppositely charged surfaces. The benefit to
the processes of absorption, adsorption, and/ this type of media is that a chemical bond is
or ion-exchange. Moe (1989) further simplifies formed when the ionized molecules touch an
this definition by stating “chemical filtration is oppositely charged surface and they become
actually mechanical filtration on a molecular firmly attached to that surface. This is great
basis.” in freshwater applications where there are
Understanding which compounds are being few anions and cations. But in seawater
removed from the solution is equally as applications, these media can become quickly
important, as different filtration techniques exhausted as they are bound up by the high
remove different compounds. Dissolved concentrations of organic molecules and
compounds accumulate through various cations, such as sodium. Fortunately, more
biological processes. And the accumulation of ion-exchange resins are being manufactured
these dissolved compounds can have serious for use in marine systems using different
effects on the inhabitants within the system. industrial processes and specific impurities
Increases in dissolved carbon-containing that affect the ion-exchange characteristics of
compounds, otherwise known as dissolved the resin.
organic compounds (DOC), such as amino Adsorption in aquaria occurs when molecules
acids, carbohydrates, fats, proteins, various are physically bound to the surface of a filter
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media or substrate. Adsorption can occur as Carbon
water to solid adsorption and/or water to gas Carbon goes by many different names. Coal,
adsorption. In either case, bonds are formed aquarium charcoal, activated carbon, and
when complex, organic, polarized molecules granular activated carbon (GAC) are just a few
or, polarized molecules with hydrophilic and of the many. Beyond the differences in names
hydrophobic ends, are attracted and attached to though, there exists a broad variety of different
a polar media and then held together by strong quality “carbons” based on how they were
or weak charges. Permanent bonds are formed manufactured. For the purpose of this chapter,
when strong attractive charges are involved, we will focus on the activated carbons as they
while bonds between weak attractive charges are the ones most used and recommended
can be broken or reversed in a process known for use in marine aquarium systems. Carbon
as desorption. An example of desorption would may take on several different forms. From fine
be the release of some organic molecules from powders to small granules, and even larger
a particular surface due to a change in pH of a pelletized forms, the way carbons function is
certain solution (Moe, 1989). the same. What may differ among these various
As in most things that have advantages to them, forms is the efficiency at which the carbons
there always seems to be some drawbacks as filter the water.
well. Concerns over the release of previously
absorbed substances, depletion of beneficial In our survey of institutions that maintained
trace elements, leaching of chemicals such as coral systems, approximately half of the
phosphate and silicate, reduction in pH and responding institutions employed the use
alkalinities, and rapid die-off caused by sudden of carbon somewhere within their display or
water clarity changes or nutrient level drop-offs filtration system, and its use far exceeded that
make up just a few of the more widely discussed of any other type of chemical filtration. In fact,
caveats that aquarists and hobbyists alike have the only other filtration method that was used in
had to deal with over the years. To help combat the coral husbandry practice more than carbon
these issues, some aquarists and hobbyists was that of foam fractionation. So you can see
have chosen to avoid using chemical filtration the use of activated carbon in coral systems
methods as much as possible, while others is common, and there are several factors that
continue to employ continuous or intermittent contribute to this result.
uses of their various types of chemical filtration.
The debate over continuous versus intermittent As mentioned previously, the most efficient
use, or even any chemical filtration use at all, chemical filters employ the use of absorption,
will undoubtedly continue to roar on for years to ion-exchange, and adsorption properties.
come as each system has its own needs and Some media are designed to incorporate
varies from the next. one or two of these properties, but few can
incorporate all three. The method in which
No chapter on chemical filtration would be activated carbon is manufactured determines
complete without the discussion of Granular how efficiently certain dissolved molecules
Activated Carbon (GAC). While GAC is are removed from solution. Carbons produced
perhaps the most commonly used type of from different coals, hardwoods, and certain
chemical filtration media, several other types other plant materials and exposed to various
of media are beginning to be used with more inorganic salts provide us with a product which
regularity. Phosphate adsorption media can be specific in the type of dissolved organic
used for the removal of inorganic phosphate molecules being removed. The manufacturing
(orthophosphate), orthophosphate precipitants process is important because different methods
such as lanthanum chloride (LaCl .5H O), ion- of manufacturing lead to differences in the
3 2
exchangers such as zeolites, synthetic ion- porosity and density of the carbon. The most
exchange resins, molecular adsorption filters/ efficient carbons are those which have a high
pads, and synthetic adsorbent polymer resins volume and low weight, are porous with large
are just some of the different media that are numbers of varying sized channels running
currently being used in coral and invertebrate through their interior, and are relatively small
systems. As with the previous section on granules of approximately 1 mm in diameter.
mechanical filtration, we will briefly discuss the This configuration provides for the largest
function, advantages, and disadvantages of surface area to remove certain molecules from
each filtration method or medium. the water. To ensure that the carbon is being
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used efficiently, it should be placed in the when that carbon is next used. Perhaps the
system so water flows through the media and most widely discussed concern over the use
not around, or over, it. of carbon in coral and invertebrate systems is
the removal of essential trace elements. There
In coral systems, there are several advantages is much speculation of carbon being such an
to using carbon. Most often, carbon is used as a efficient chemical filtration media, that essential
water polisher to remove the DOC responsible elements needed for the survival, growth, and
for the yellow color that forms over time. This reproduction of corals, clams, and invertebrates
allows for increased light penetration throughout may be taken up before they are able to be
the system. In addition to the removal of used by these animals. The rapid removal of
yellowing agents, carbon removes odor-forming yellowing agents in system water can also
organic molecules, toxic organic molecules, contribute to die-offs or bleaching events in
and some heavy metals. Arsenic, chromium, corals and clams due to sudden increases in
silver, mercury, iron, lead, nickel, titanium, light intensity. There is speculation that the
copper, zinc, molybdenum, manganese, and use of carbon may affect head and lateral line
tungsten are just a few of the heavy metals erosion (HLLE) as either a result of removing
which may be removed through the use of some essential element needed by that animal,
activated carbon (Sigworth and Smith, 1972). or by possibly introducing some compound or
Sigworth and Smith (1972) concluded that even microscopic carbon particles that lead to
activated carbon could be used to purify water the onset of the HLLE (Delbeek and Sprung,
of trace metals and other compounds under the 2005; Hemdal, pers. com.).
proper conditions. However these conditions
had very little relation to the conditions found It is possible that carbon, when used in systems
in coral systems. The mechanism by which along with ozone, may be pulverized into fine
these metals and others are removed by particles which may affect the inhabitants
carbon is still largely misunderstood, but in within the system. But the authors could find
marine systems some metals may be removed no evidence of this happening in coral and
when the organic molecules to which they are invertebrate systems. This may be a result of
bound are adsorbed by the carbon (www6). the decreased dosage run on sensitive coral
Some salt mixes, food items, and even some systems. And cases where this has happened
source waters can elevate concentrations of may have been on systems using higher
these molecules, and the use of carbon can dosages of ozone that contained larger and
help keep these concentrations at manageable hardier vertebrates. In any case, care should
levels. High volumes and low production costs be taken when combining these two filtration
make carbon an easy media to replace. It techniques. And further studies should be
can be recharged to an extent, however this performed to identify any additional negative
method is largely inefficient, time constraining, interactions between the two media.
sometimes costly and, therefore, rarely used.
The advantages and disadvantages of using
Possible disadvantages carbon vary from system to system. Because
Some doubts do exist throughout the industry systems vary so much from one another, it is
over the usefulness of carbon within coral and difficult to recommend one general guideline
invertebrate systems. There are concerns for its usage. Observation of the animals in the
over the possible release of phosphates and system is a must when trying to decide how
inorganic salts (www2). There is currently much often and how much carbon, if any, is to be
debate over the likelihood of this occurrence. used. It can be used constantly, intermittently,
Activated carbon is a great absorbent. But or not at all. Larger amounts can be used and
once all the pores and surfaces have become changed less frequently, or smaller amounts
exhausted, the possibility of previously can be used and changed with more regularity.
absorbed substances being released back The aquarist needs to keep in mind that carbon
into the water does exist (Spotte, 1979). Even is susceptible to bio-fouling. And the more
outside the system, toxic substances can be biofilm that clogs each granule’s pores, the
absorbed if they, and the carbon, are not stored less efficient that carbon becomes. If carbon is
properly. Because absorbed molecules are not not employed, then other methods of removing
bound to the surface, there stands a chance dissolved organic molecules and other non-
that they can be released into the system desirable compounds should be used. Sudden
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changes in water clarity can be avoided by than most carbon particles, and they easily slip
changing carbon media frequently before through holes in filters designed for use with
yellowing molecules begin to accumulate. carbon. Filter bags can be used to hold the
Using smaller amounts of carbon can also media, but frequent cleaning of the bags must
prevent essential elements from being depleted occur to prevent the mesh from being clogged
too quickly. Frequent changing of carbon with biofilms.
before the media is exhausted can prevent
the release of previously absorbed molecules. Phosphate adsorption media
Another frequent concern is how the aquarist The accumulation of phosphate in coral and
knows when to change the carbon within the invertebrate systems has become a growing
system. Spotte (1979) suggests that carbon concern among aquarists as we continue to
be changed every 8 weeks or when desorption learn more about its affects on the calcification
begins to occur. By monitoring TOC levels the of corals, clams, and certain calcareous algaes.
aquarist can determine when equilibrium is In addition, phosphates serve as fertilizers
reached, and then change the carbon. More for certain undesirable types of algae which,
often a visual cue is used to determine when when allowed to accumulate, may lead to algal
the carbon should be changed. A quick indicator blooms and reduced water clarity. While some
of carbon exhaustion is yellowing of the system measures can be taken to minimize this trend,
water. Finally, there are ways to test carbon such as using phosphate-free salt mixes and
media to determine if they are, in fact, releasing carbon, and reducing feedings and rinsing
phosphates or silicates into system water. And feed items before introduction into the system,
phosphate/silicate free varieties of carbon are the trend for increasing phosphate levels
advertised to prevent this occurrence. continues. Two main phosphate adsorption
materials have become available over the last
Synthetic polymer adsorption media few years to help control this problem. Both can
In an attempt to improve upon the chemical be used continually, intermittently, or not at all.
filtration properties of carbon, companies have Care should be taken when used intermittently
manufactured synthetic polymer resins that as some of these adsorptive media may affect
allegedly perform most or all the same desirable water clarity and affect the health of the coral
characteristics of carbon while trying to limit and invertebrates.
the adsorption of essential elements within the
system water. These are most commonly found Aluminum oxide
in the form of small plastic resin beads or filter Chemical filtration media consisting of
pads. As with carbon, they can be manufactured aluminium oxide (Al O ) have proven
2 3
to remove specific dissolved organic molecules themselves to be reasonable adsorption media
and metals depending on your system needs. for the reduction of phosphate levels in reef
aquaria. These media are most often found
These media can be used continually, in the form of small beads, and are contained
intermittently, or not at all. Water flow should within fine meshed media bags. They can be
be passed through the media to ensure placed in contact chambers to help facilitate
maximum adsorption efficiency. The benefits water movement through the media or they
of these media may include adsorption of can be utilized passively in a sump. Aluminium
yellowing compounds, removal of nitrogenous oxide-coated pads can also be found which are
compounds, removal of phosphate, heavy simply placed in an area of the system which
metals, polar organics and inorganic salts. then passes water through the pad.
There are little or no irritating dust particles, a
color change is often noticed when the medium Possible disadvantages
has been exhausted and, in some instances, While tests have been performed showing that
the medium can be recharged and reused. these media do help reduce phosphate levels
in coral systems, the release of aluminum
Possible disadvantages from some of these media into the system
These media do usually carry a higher price for has also been noticed. It is not widely known
far less volume than that of carbon. In addition, what, if any, negative effects the release of this
finding ways to incorporate these media aluminum may have on corals, but Holmes-
into your filtration system may require some Farley (www3) performed one experiment
creativity. The resin beads are usually smaller on soft corals using additions of aluminum
92
chaPTeR 10: abioTic filTRaTion meThods foR live coRal sysTems in Public aquaRia
chloride to observe any negative interactions reaction occurs suddenly, it is recommended
that may occur. This experiment showed that that lanthanum chloride be added slowly and
the addition of aluminum chloride to a coral in small quantities. Lanthanum chloride powder
system resulted in corals with reduced tissue can be mixed with reverse osmosis (RO) water
and polyp expansion. But it was also concluded or it can be obtained already in a liquid form.
that further testing would be needed to confirm The use of a drip system is one of the easiest
that these results were, indeed, caused by the ways to add lanthanum chloride, in a slow and
addition of aluminum. controlled manner, to the system (Collins, pers.
com.). Use of this chemical can be employed
Iron oxide continuously as a way to control phosphate
More recently, granular forms of ferric iron oxide levels or intermittently, when phosphate levels
(Fe O ) or filter pads coated with the ferric iron begin to rise.
2 3
product have come into use for the removal
of phosphate from coral and invertebrate Possible disadvantages
systems. These media are efficient adsorbents While the proper use of lanthanum chloride
of phosphate and are capable of lowering has been shown to greatly reduce phosphate
phosphate concentrations to much more levels in fish, elasmobranch, invertebrate, and
manageable and natural levels. Once bound to other marine systems, it is equally important
the media, the adsorption properties of these to understand the disadvantages associated
media keep the phosphate firmly in place until with this chemical and its misuse. Water
the removal of the media from the system takes quality problems such as sudden drops in pH
place. As with aluminum oxide, these media and alkalinity levels are the most commonly
can be placed in contact chambers or within discussed issues associated with the use
a sump or other area where water is actively of lanthanum chloride. Close monitoring of
passed through the media. One increasingly these levels should be performed. Often these
common method for using this media involves drops are the result of adding the chemical too
applying it to a canister or reactor chamber in quickly, or in too great a quantity. By adding the
a reverse flow situation. Care should be taken flocculant slowly and bringing the phosphate
that it does not become fluidized as the media levels down gradually over time, it may be
will crumble upon itself (Yaiullo, pers. com.). possible to limit the extent of these drops.
Another disadvantage of this type of misuse
Possible disadvantages is clouding of the water and the formation of
Care should be taken when applying the use of a lanthanum phosphate precipitate all over the
iron oxide in coral systems. Reports of reduction system being dosed. This coating could have
in pH and alkalinity have been made and have disastrous effects on sensitive invertebrates
been attributed to the possible binding of such as corals and clams. In addition to the
calcium carbonate to the media (www4). Direct stress placed on animals within this system,
side effects of the addition of these iron oxides additional time and energy must then be spent
on corals have not been heavily reported, to remove the coating from system windows,
but close monitoring should be performed to rockwork, and life support systems. Careful
prevent sudden pH and alkalinity drops. It has attention should also be paid to the filtration
been suggested that calcium and alkalinity on the system while the lanthanum chloride is
supplements be added as far from these media being used. Increased loads on sand filters,
as possible to help avoid precipitation and bag filters, paper cartridges, etc may drastically
caking of the media (Yaiullo, pers. com.). decrease flow within the system. And these
mechanical filters may need to be cleaned
Phosphate flocculants before, during, and after using this, or any,
In addition to phosphate adsorbents, phosphate flocculant.
precipitants, such as lanthanum chloride, can
be used as phosphate removal media. As Because lanthanum has affinity for both
discussed earlier, this chemical is most often phosphate and carbonate, there is a relative
used in conjunction with rapid sand filtration. increase in alkalinity removal as phosphate
In systems where RSF are not in use, the use levels decrease. So the aquarist must evaluate
of some other form of mechanical filtration is where the cost of adding alkalinity exceeds the
necessary to remove the solid, lanthanum benefit of phosphate removal (Curlee, pers.
phosphate, which is formed. Because this com.).
93
R. TeRRell, JR., R. KlobuchaR, JR. & c. PRaTT
Ion-exchangers ultrAvIolet sterIlIzAtIon
Though rarely used in marine systems, some
ion-exchange minerals do exist which claim Ultraviolet (UV) sterilizers have been used on
to benefit coral and invertebrate systems. freshwater and marine fish-only systems for
These ion-exchange minerals, or zeolites, are many years. In many cases, their use in outdoor
most commonly used in freshwater systems applications served simply to clarify water that
where they are not as susceptible to becoming had become overgrown by algae within the water
bound and exhausted by the large numbers column. In aquaculture facilities, UV sterilizers
of ions present in seawater. The few marine provide a chemical-free way of treating water
manufactured varieties of zeolites which are entering the systems as well as help reduce the
available claim to remove some nitrogenous spread of free swimming disease organisms.
materials, thereby reducing the concentration Regardless of what goal they are intended to
of dissolved organic compounds within the be used for, the process by which they work
system. remains the same. UV sterilizers are filtration
One such zeolite being manufactured for coral devices which produce certain wavelengths of
systems is ZEOvit (www7). According to their light to achieve their filtration goals. Chemically
website, ZEOvit is actually a mixture of several speaking, UV sterilizers are effective in that
different zeolites which were chosen based on they break down and alter cells on a molecular
their ability to reduce certain toxins in a balanced basis by this light. Moe (1989) states that UV
manner. ZEOvit claims that it permanently sterilizers work by emitting certain wavelengths
absorbs ammonium and ammonia, which then of light which alter the genetic makeup of DNA
prevents the formation of nitrite and nitrate. within the cells passing through the unit or by
Other benefits of using ZEOvit may include creating oxidants or other toxins in the nearby
improved water clarity, improved coral tissue vicinity or within the cells.
expansion, brighter coral coloration, and faster
coral growth rates when used as directed The effectiveness of UV sterilizers is controlled
and in conjunction with carbon and certain by many factors. The wattage of the UV bulbs
supplements. being used and the flow rate through the unit
are two of the main considerations to take into
Possible disadvantages account when deciding which unit to use. These
Like carbon, zeolites share certain absorption two factors play a large role in establishing the
and adsorption properties which may deplete efficiency of each UV sterilizer. In addition, it is
certain essential elements from a system. Many important to identify the target organisms that
of these elements are essential for coral health the aquarist hopes to kill. Certain organisms
and growth, thus frequent supplementation will tolerate higher levels of UV irradiation than
be needed to replace those elements bound others. Once the target organism is identified,
up by the zeolites. Zeolites are also easily the aquarist can identify the proper “zap
exhausted, and it is recommended that they dosage” needed to kill this organism, and
are replaced frequently. ZEOvit recommends choose a unit capable of achieving this goal.
replacement every 6-12 weeks (www7). When Escobal (2000) defines the zap dosage as that
compared to the costs of replacing carbon, this which is required to achieve a 100 % kill of the
can become an expensive endeavor, especially targeted organism through the UV sterilizer.
on larger systems. Problems can also arise as a While higher wattage units can be employed in
result of overdosing zeolites. The rapid change attempts to guarantee targeted organisms are
in nutrient conditions and sudden increased destroyed, this is one situation in which size is
water clarity can lead to tissue loss on SPS not crucial. The goal is to ensure that at least
corals. This may range from tissue recession two full water exchanges pass through the unit
along the tips of the corals to the complete loss per day. With this in mind, passing too much
of all coral tissue within a short period of time. water through the unit decreases the contact
time during which the targeted organisms are
While the zeolites used in ZEOvit and other exposed to the UV light. An efficient 100 % kill
products do exhibit some absorption and may not be reached by the time the cell exits
adsorption properties, it appears that these the unit. The best way to control this is to install
products benefit the system more from their the unit inline with a series of control valves and
biological filtration properties than their chemical bypass(es) because the delivered dosage is
filtration properties. flowrate-dependent (Escobal 2000). Flow rates
94