View Full Version : So you want to understand filtration and methods
10/20/1999, 05:07 PM
This is in response to Larry's request for topics.
I thought it would be useful to discuss the three types of filtration in a reef tank (biological, chemical, and mechanical) and the ways each are accomplished.
10/20/1999, 05:21 PM
Biological filtration is basically the process where waste products are removed from the aquarium through the interaction with bacteria. The bad wastes are converted by bacteria into either nitrogen gas (the process of denitrification) or nitrates (nitrification).
(I suppose another topic could be on the chemical processes in the aquarium)
Anyway, there are several methods of biological filtration: undergravel filters, wet-dry/trickle filters, and live rock.
Somebody else take it from here :)
10/20/1999, 06:10 PM
I've tried using canister filters, wet/drys with trickle filters containing bio-balls, Bio-wheels, and live rock for salt water filtration. While they all work, IMO live rock is the way to go, especially for a reef tank. It is not cheap, but then the hobby in general is not cheap. I still use a trickle filter with bio-balls on my FO tank because I'm afraid the live rock couldn't handle the bio-load--but I'm probably wrong about that.
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10/20/1999, 06:52 PM
Protien skimmers are considered required equipment, at least in the start up phase, though some people choose not to run them after the tank stabilizes and they have a good grasp of the processes involved. FAQ is a skimmer needed on Fish Only tank and a common responce is no you only need them on reef tanks. Personally I feel FO tanks will definatly benefit from skimming. Skimmers are simply a column of water which is filled with zillions of tiny bubbles, Dissolved Organic Compounds and other waste will attach to the bubbles and be carried up the water column and into the collection cup. The benefit is the waste is removed from the water rather than trapped to by broken down by bacterial action so it reduces the load on ather filtration whether is Live rock/sand, Wet/dry/ Biowheels etc. Given that fish produce more waste than an equal amount of invert biomass due to feeding and waste plus the higher rate of urination to achieve osmotic balance a good skimmer will remove a lot of this before it gets trapped, contributing to lower nitrate levels and increased water quality.
On small systems you can get by with frequent water changes but the cost and effort increases as the size of the system does.
I reefed,so I spent,it would have been cheaper to do it right the first time.........Doug@thereeftank
10/20/1999, 08:01 PM
Great comments guys :)
Larry, how about a quick-down-and-dirty explanation of what a wet/dry is, why it works, and why it may not be best for a reef (as opposed to LR).
Also, if someone wants a FO and doesn't want to buy live rock, is a wet/dry the best option or why would someone maybe prefer an undergravel filter.
Thanks Professor Larry :)
10/20/1999, 08:16 PM
There are people better qualified to answer that than me, Brian. Why do you think I glossed over it the first time? LOL
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10/20/1999, 08:53 PM
Biological filtration is the conversion of toxic waste products (mainly ammonia NH3/ammonium-NH4+) in the aquarium to either less toxic or non-toxic forms. There are two main processes that occur in a bacterially based system: denitrification (conversion to non-toxic nitrogen gas-N2) or nitrification (conversion to the less toxic form NO3).
Nitrification (conversion of Ammonia to Nitrate) occurs through a two step process that is dependent on two types of bacteria. The first step involves the oxidation of NH3 to nitrite (NO2) and is facilitated by nitrosommonas bacteria. The second step occurs through the oxidation of nitrite to nitrate (NO3) and is facilitated by nitrobacter bacteria. Both of these steps require an aerobic environment (that environment which is rich in oxygen) in order to oxidize NH3 to the final less toxic NO3 form. Without bacterial denitrification or plant based ammonia fixation, nitrate will accumulate within the aquaria until it will need to be exported through water changes. Although nitrate is less toxic to inhabitants, it is still toxic and should be kept at acceptable levels.
Denitrification occurs in anaerobic environments (those areas with low or no oxygen). It involves taking nitrate (or ammonia directly) and reducing it to a completely non-toxic form-nitrogen gas. Denitrification can occur to some extent in an aerobic environment; however, an anaerobic environment must be provided for efficient denitrification to occur. Denitrifcation can be accomplished by a number of bacteria; however, Thiobacillis is one of the more common. Problems with denitrification can occur when Thiobacillis (Thio=sulfur) generates pockets of hydrogen sulfide (H2S)during the reduction processes. H2S can be identified by a rotten egg smell and black zones within sand beds. Because H2S is toxic these zones should not be disturbed as they will generally resolve themselves.
A third form of biological fixation is the plant based system in which ammonia is converted to nitrogen gas through nitrogen fixation processes. These systems have been popular in freshwater aquaria for since their inception, and have been becoming an additional facet of marine aquaria as of late. The disadvantage of this system in marine aquaria is that the more popular fish (namely tangs and other omni or herbivorous fish) can dessimate a macroalgae population rapidly unless it is kept within a refugium.
The biological systems:
While there are several choices for setting up a biological system, they are based on two basic methods: 1)a natural system of live rock and sand based substrate or 2)a medium for bacteria to proliferate on in an aerobic environment (wet-dry/biowheel/biobale/etc).
The general benifits of the natural methods (Live rock/sand) are several fold: Firstly, using live rock (aerobic and anaerobic) and a deep sand bed (anaerobic environment after the first few inches), you can provide for both nitrification and denitrification processes. Both of these processes are not simultaneously possible in the aerobic environment of wetdrys/biowheels. Therefore, in a properly established natural system, the nitrate does not accumulate as rapidly, if at all. This prevents problems of nitrate toxicity as well as algae problems associated with increased nitrate levels. Furthermore, LR in itself has anaerobic zones which permits some dentrification to occur in the absence of the deep sand bed. Second, LR/LS provides for increased diversity and environment that is similar to the natural systems. Third, LR/LS provide a chemical buffer for the aquaria, protecting against pH swings. Fourth, (my opinion) LR/LS is more aesthetically pleasing and natural.
The bacteria: Despite manufacturer's suggestions otherwise, stabalization of nitrobacter in a dormant state on LFS shelves is difficult and generally results in a significant loss of bacteria. Freeze dried nitrobacter is very difficult to keep viable-so these products should be avoided as a rapid cycle method. Nitrosomonas is more amenable to these processes; however, this only gets you half way there. Denitrification bacteria are available and are quite effective-especially if there are anaerobic zones-such as sand beds within the aquaria; however, generally these bacteria require a carbon or sulfur based food in order to carry out their processes efficiently. B/c of their diverse nature, properly maintained sand beds usually are capable of providing these necessities without further input.
One of the single most important components in chemical filtration is the protein skimmer. It provides the removal of dissolved organic compounds (DOC)-including proteins that can result in the direct accumulation of nitrates and phosphates. Most skimmers also provide the aquarium with a degree of particulate skimming and therefore provide some mechanical filtration benifit. There are several factors that affect protein skimming efficiency (irreguardless of the skimmer model)-1) the amount of air delivered into the reaction column; 2)the contact time of that air with a given volume of water; 3) the size of the air bubbles (the smaller the better); 4) the dissolved salt content in the water.
Activated carbon also affords some degree of DOC removal, and can be an important form of chemical filtration. Activated carbon when used intermittently will polish the water by removing yellowing compounds and DOC. It will also remove harsh and harmful chemicals/toxins quite effectively. The disadvantage to continuous use is that it is so efficient in its function, it removes important trace elements from the system that would need to be constantly replinished. Phosphate removers on the market also probably fall under chemical filtration. These are generally aluminum based and despite some manufacturers claims can not be easily regenerated in the home. Although these resins can be quite effective at binding phosphate, they are generally only good at lowering phosphate levels a few points, and therefore, other methods should be employed to get the levels down (ie. water changes, watching their introduction) prior to the use of these resins.
UV filtration is also a chemical filter that may wish to be employed intermittently after the addition of new specimens or on disease outbreak, but most likely should not be run continuously b/c it destroys benificial free swimming life, bacteria, etc.
Mechanical Filtration: Although mechanical filtration does provide a degree of effectiveness in the aquaria for removal of undesirables-IMHO continuous use does more to cause problems than it does good in a reef aquaria. Firstly, mechanical filtration traps and removes many planktonic life forms from circulation. These lifeforms are quite importnat for the maintenace of many corals and fish species. Second, accumulation of detritus within mechanical filtration if not regularly cleaned provides a significant source for the breakdown of these substances and the accumulation of nitrates.
10/20/1999, 08:56 PM
hi. i realize that liverock is probably the best way to go for filtration, but i really don't want that look for my tank. i was reading through a pet warehouse catolog and noticed this filter media called siporax. it claims to not only remove nitrites but also nitrates. does any one have any comments on this media? thanx for your time.
10/21/1999, 09:55 AM
Lee-I use Siporax in my q-tank in a small submersible power filter to nitrify the ammonia. IMHO Siporax (sintered glass)is probably comparable to activated carbon in that it too is full of micropores, sites for microbial colonization, such that a small amount can hold a LOT of bacteria. If you kept a container of siporax in a low oxygen environment (i.e. a slow flow filter where water is dripped in one end and out the other into your sump) it could act as a denitrifying filter provided you vent off the accumulated nitrogen gas somehow.fwiw, kas
10/21/1999, 11:02 AM
Does anyone have any experience with Cell-Pore in any of their tanks?
10/21/1999, 01:06 PM
Ignatz, just added some of the Cell-Pore 1" blocks in a canister filter I am using. The water flow through this filter is relatively slow. Supposedly, in a minimal flow environment, the cell pore media will provide denitrification along with bio- filtration. Don't know if this is the case, but will hopefully find out. I spoke with the folks at Cell Pore and they recommended the bigger blocks for denitrification.
One thing that is neat about Cell Pore is that it is very porous. I held one of the blocks under a running faucet and the flow is virtually identical with or without the Cell Pore.
Will give an update once it breaks in.....
10/24/1999, 05:59 PM
Are we done with this?
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