biological filter

Question
I have a 29 gallon fish tank.  I have mollies, guppies, albino catfish, and tetras in the fish tank.  I am using a 30 - 60 gallon filter that has two biological filters along with the charcoal filters.  My water is looking real nasty so I changed the water and cleaned the tank.  This did not help, so I checked my biological filters and they were full of guck/bacteria.  I don't know what was on them. I took one of the filters and cleaned it.  I am wondering if this is the right thing to do, do I need to clean the biological filters ever so many months along with the charcoal filters.  I know that healthy bacteria grow on the filters  and I don't want to kill the healthy bacteria.  When I cleaned the one bio filter, my tank cleared up.
What do I need to do about the bio filters.  Any help would be appreciated

Answer
Hi,
Replacing the carbon should help. Replace these every other month, but alternate so you are replacing 1 every month.

For the bio aspect, syphon out about a gallon of aquarium water into a bucket. Scrub the bio media in this water and put it back into the filter. This will not kill or remove the nitrifying bacteria, but will remove every thing else.