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Back to Basics: A Look at Filtration, Part 3 - Chemical Filtration and Two Specialty Filters

By:  Karen Randall, BAS
Published in The Daphnian, March, 1991

Well, after a hiatus of several months, we’ll try to finish up our series on filtration.  As a reminder, we covered biological filtration in the June 1990 column, and mechanical filters in the following issue.

Chemical filtration can be a useful adjunct to the other forms of filtration.  They will not, however serve as a replacement for either biologic or mechanical filers.  Nor will they alleviate the need for regular water changes.

Probably the most prevalent form of chemical filtration is the use of activated carbon inside a mechanical filter.  As the water flows through the carbon, various dissolved wastes are absorbed.  Carbon is particularly good at absorbing the chemicals that turn tank water yellow in aquariums that have been set up for a while.  It will also remove trace amounts of harmful chemicals that may be inadvertently introduced to the tank.

As is true with most substances used for chemical filtration, carbon has a fairly short useful life before it has absorbed as much as it can.  It is, however, readily available and relatively inexpensive, so many people add new carbon to their mechanical filters with each cleaning.  Remember to rinse carbon thoroughly before putting it in the filter.  It is very dusty, and unless well rinsed, it will turn your tank, at least temporarily, into a black cloudy mess.

Carbon is easier to handle if it is encased in a mesh bag that can be placed inside the filter, and refilled with a fresh supply as needed.  Some manufacturers sell carbon cartridges specifically designed for use with their filters.  These are certainly convenient, but are more expensive than buying loose carbon.  You can buy cartridges of carbon to fit on the uplift tubes or some under gravel filters, but in my opinion, these hold too little carbon for a meaningful contribution to the water quality in the tank.

Another method of using carbon is to introduce a powdered form mixed with diatom powder to a diatom filter.  This method can be very useful for quick damage control.  I once had a freshly flea powdered kitten fall into my 70 gallon display tank while the cover was open during routine maintenance.  After doing a 50% water change, I ran my diatom filter with carbon for an hour.  I did the same thing the following day, and lost only a couple of fish, in spite of having introduced poison directly into the tank.  Of course it would have been better to keep the kitten out of the tank, but accidents do happen!

One important point to keep in mind is that carbon will remove many types of medication from the water.  So it should not be used in a hospital tank.  If you need to treat your entire display tank for an illness, remember to remove the carbon from the filter first.

There are products on the market which will reduce or eliminate the ammonia in your tank.  The manufacturer suggests adding this substance to your filter on a regular basis.  It is available in a granular form that can be handled in the same way as carbon, or it can be purchased pre-mixed with carbon.  It is also available in impregnated pads that can be recharged and reused.

I personally don’t like the idea of running it in a tank on a regular basis, because if you are properly managing your biological filter, there should not be any measurable ammonia in your tank to start with.  A certain amount of ammonia must be available to feed the beneficial bacteria in the tank.  If you artificially reduce the ammonia available on a regular basis, I suspect that the ammonia would spike when the filtering medium reached saturation.

A more appropriate use of this substance would, again, be disaster control.  If for some reason your tank experiences a temporary ammonia problem, water changes plus running an ammonia reducing agent in your filter should remove the ammonia from the water while you rectify the cause of the problem.  (such as pulling that dead fish out from behind the heater).

If your water department uses chloramine rather than chlorine, you can use this product in conjunction with a dechlorinating agent to treat the water you need for your tanks.

There are resins available that can be used to soften hard water.  As the water flows through these resins, the calcium carbonate in the water is replaced by sodium chloride.  The resin then can be recharged by soaking it in a strong salt solution.  Just remember, there are fish that will not tolerate salt in their water any better than they tolerate hard water.

Another, more natural, method of softening water and at the same time lowering the pH, is to filter it through peat.  Many breeders swear by this method.  The main problem with peat is that it also turns the water brown.

Most community type fish can adjust to moderate amounts of hardness and/or salt in their water.  If you are intending to breed fish that require very soft water, and peat won’t do the trick, you will probably have to reduce the hardness of the water by adding distilled water, or by investing in a reverse osmosis unit.  Although I suppose reverse osmosis is more of a mechanical procedure.  I mention it here because it is used to remove hardening substances from the water.  It is a specialized piece of equipment well beyond the needs of the average hobbyist.

The last piece of equipment on the market that I would like to mention is the protein skimmer.  These are used on marine aquariums, and like the reverse osmosis unit, they are probably beyond the needs of the average hobbyist, although unlike the reverse osmosis unit, there are small, inexpensive models available.

Proteinaceous waste products form a skim at the point where water and air interface.  The protein skimmer takes advantage of that by creating extra surface area in the form of tiny air bubbles in a narrow tube.  The bubbles are coated with the waste material in the water, and burst in a collection chamber at the top of the tube.  The hobbyist then is able to remove these wastes from the tank by emptying this chamber.  Protein skimmers range from fairly inexpensive mechanical devices placed in the tank and run with a small air pump to large motor driven models that run outside the tank in line with other forms of filtration.