We have had a 16-gallon aquarium for just over one year.  We have also have had a 48-gallon aquarium for about 6 months.  Both have filter that operate on top of the tank next to the lighting unit.  We were told not to change the filter wool as it would take away important bacteria from the tanks.  However, we would like to know when and how it would be okay to change the wool in our 2 tanks.  The wool has become extremely polluted and has been rinsed out with the tank water weekly or biweekly since we have had them.  When is it okay to replace them?  Should we replace one piece of wool in each tank at a time?  If so, how long should we wait before changing the second piece?

Your advice is appreciated!


You should only change one piece at a time and wait at least a period of about 4 weeks before you replace the other one to allow the bacteria to culture on the new one. Then if you want to you can set up a schedule to change maybe a piece every 4 weeks if you would feel that it would not be as "polluted" In no case should you ever replace the whole thing at once though, I agree.



My HOB (hang on back) filters have the filter media that you fill them with carbon and then slide the filter on a slot, and the water runs through it. Unless you are having restricted water flow through your wool, don't change it. Just continue to rinse with old tank water. I've had mine running at least 6 months without ever changing the filter media. When you do have to change it, save a piece if it, and put this piece inside the pouch if it has one, or place it behind the new wool, so the bacteria can grow faster on your new wool and not cause your tank to have a minI cycle. If you have 2 filters working in the same tank, you can change the media out alternately between filters. That way you will always have established media in one of the filters.

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