Internal Filter

Question
Hi Karen
I went to my local fish shop today and we were talking about filters.  I have a 47.5 gallon setup that came complete from Fluval.  Included in it was a Fluval 4+ internal filter.  My tank is around 11 weeks old now.  The problem I am seeing is that about every two weeks I have to empty some tank water into a bucket and clean my sponges as the flow out of the top of the Fluval has reduced to a trickle.  The sponges are always clogged at the top with black sludge.  The man at the Local Fish Shop says I should leave the filter as it will unclog itself and I am washing away beneficial bacteria.
Do you have any view on this.

Many thanks

Jon

Answer
Hi Jon,
No you aren't washing away beneficial bacteria! If you leave the sponges to clog and the fluval to run at a trickle you can also cause a very bad deal of anerobic bacteria. Or course anerobic means (thrives in low-zero oxygen enviroment) which is triggered by a very slow flow of water or a totally clogged filter. These bacteria are somewhat good as they control nitrates.....But they also produce very toxic gas in your aquarium water that can quickly be EXTREMELY harmful to all your fish and also make your aquarium water smell like rotten eggs! This doesn't happen everytime...But it can happen and it does. All in all your beneficial bacteria need oxygen rich water flowing over them at all times in your sponge filters.
Not to mention you need to clean the sludge from the sponges frequently as this sludge is just trapped waste or food and needs to be removed from the aquarium (that's what the sponges are for anyway!) or they will dissolve after a while and pollute the aquarium all over again.

So all in all. The simple real answer contrary this from the fish shop man's advice is--clean your filters. Your beneficial bacteria will NOT be harmed by washing the sponges in your TANK water. The only surefire way to harm them is to rinse them in tap water where the chlorine will destroy them. Keep doing what you're doing. You're doing it right I know.

Well, I hope this helps! Feel free as always to write if you have anymore questions or concerns.
Best wishes and Take care,
Happy fishkeeping!
Karen~