Here's a tip about cleaning filters that I learnt.
Always clean the filter media with the water you have taken out of the tank,
never use clean tapwater to clean it, it kills off all the good bacteria that is needed in the tank.
Also depending on your filter and how many sorts of filter media you can put in it, try and fit a bag of charcoal in, not the stuff for BBQ's though
You can buy it in filter bags at all good aquatic shops. I used to put 4 types of media in mine, ceramic tubes, coarse sponge, fine sponge (like cotton wool) and carbon - in that order.