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  About Filters


After water, filters are the most important piece of equipment required to keep an aquariums' inhabitants alive! It doesn't matter whether the filters are undergravel, external canister, internal, or any variation of the above. Filters have one primary purpose in an aquarium and it is to process the waste generated in that aquarium. For that reason they are often referred to as biological filters. The waste comes from the fish, through their breathing, expelling waste through their skin and droppings, from decaying food and plant life and possibly the occasional dead inhabitant.



ALL animals, including humans produce waste which is processed quickly by 'unfriendly' bacteria, producing AMMONIA. It is what you smell when an animal's cage is not regularly cleaned out, it is that sharp smell. It also happens in an aquarium and ammonia over certain concentrations is toxic to fish. In nature there is always a balance (until humans come along and destroy it). What is waste to one animal is food for another. The filter media in your filter is designed to culture and house vast numbers of friendly bacteria which eat ammonia. Their waste is a product called NITRITE which is also toxic to fish. Another type of bacteria (called nitrifying bacteria) then eats the nitrite and their waste is NITRATE, which IS harmless to fish. Your live plants then absorb the nitrates as food and the cycle is complete!


A new aquarium and filter does not have enough friendly bacteria to process the fish waste. It can take up to SIX WEEKS, without assistance, before there is enough friendly bacteria. This is a critical period in the life of an aquarium. It is when all the fish that seemed OK for the first few weeks suddenly seem keen on dying. If you have packed the new aquarium with fish you will have a lot more problems than someone who knows about the waste cycle and only puts a few fish in. It is a catch 22 situation, you need the fish to produce the waste so bacteria can start colonising the filter media, but if too much ammonia is produced too soon problems develop. Help is at hand. First there are products such as STRESSZYME which is a concentrated source of friendly bacteria which greatly speeds up the colonisation in the filter. There are test kits which can tell you now many PPM (parts per million) of ammonia, nitrite, and nitrate you have in the aquarium. If the ammonia level gets too bad (over 3 PPM) you do a partial water change (25%) and retest. Eventually, after a few weeks you will have a 0 PPM ammonia reading and a slowly increasing nitrate level, at which time you will know you filter is coping with the ammonia being produced.


You may find that the water in a new aquarium starts to go cloudy after you start adding the bacteria. This is called a 'bacterial bloom'. More bacteria are being produced than is necessary. Continue to add Stress-Zyme and monitor the ammonia, and you will find that the water eventually clears after a few days, as the bacteria balance themselves to the amount of ammonia being produced.

 If you add a lot more fish then you need to monitor the ammonia levels again, and also if say a large fish dies and starts to decompose in the aquarium before it is noticed.

There are products such as AMMO-LOCK which locks up ammonia and converts it to a non-toxic form until the filter has time to catch up if you have had a major problem, or can't change the water to reduce an ammonia buildup.

If you sniff the water of an aquarium and can detect even the slightest sharpness you can bet the ammonia level is too high.

When you clean out your filter, you obviously want to keep enough of the bacteria you have spent so much time culturing, so this is the correct way. If your filter has foam and/or hard material it needs to be cleaned in some of the aquarium water it has been filtering. This means the bacteria are not shocked by a change of temperature, pH or a sudden dose of chlorine from fresh tapwater (chlorine is in tapwater to kill bacteria if you didn't know) . Syphon out some water into a bucket for this purpose. The media doesn't have to be cleaned spotlessly, if the filter is the correct size for the aquarium it will soon sort out any cloudiness caused by you disturbing the filter media. A squirt of STRESSZYME in the aquarium can also soon make up for any lost bacteria.

If the filter is the correct type and size for the aquarium you shouldn't need to clean out the filter more than once every 6 months! A lot of factors can affect this however, overcrowding the aquarium, too much light, overfeeding are just the obvious ones. You should be able to see now that you can never OVER FILTER an aquarium but you can certainly UNDER FILTER one.

The by-product (waste) from the filter is nitrates. It is unlikely you would have enough plants to absorb all the nitrate. This is where water changes come in. It is to reduce the amount of nitrates in the water. Otherwise the water will take on a yellow/brown tinge that no amount of filtering will remove. Also although most fish tolerate very high concentrations of nitrates some don't. More importantly, green algae loves nitrate rich water. Use your nitrate test kit to monitor the levels so you can adjust the amount of water change to keep the nitrate level at 20-30 PPM.

There are various special filter media you can put in your filter to achieve certain desired results. The most common is activated carbon which is put in for a short time to absorb perhaps medications that have been used, or to polish the water for extra clarity. There are also various resins designed to absorb nitrates if you are unable to do regular water changes or want to continually strip nutrients out of the water as they are being produced.


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