I have over the back hanging filters for my two 2 gallon aquariums. Sometimes a little sludge gets stuck on the plastic that the filter cartridge sits in. I normally clean this off in the sink. Not back into the tank.I received two conflicting answers from the same Pet Store Chain, but from two different stores.One told me to wash it off.The other, told my husband that this is good bacteria and shouldn't be removed.My Ammonia levels are good and tanks are clear. I have photos of the sludge I can upload tonight.It is a darkish green/brown in color.Opinions? Thank you.