If you do a WC does the water just cloud back up? If so you are having a bacterial bloom which can be caused when the substrate is disturbed a lot, among other things. Bacterial blooms normally run their course and clear up in a matter of days. If you just have a lot of very small, fine detritus particles in the water then you can get a cheap bag of 100% polyfill which can be bought at Walgreens, Target, or any craft store. Just stuff it into your filter where there is room. The dirtier the polyfill gets the smaller the particles it will filter out of the water. When it's dirty, just throw it away and add new.
A bacterial bloom will not be filtered out by filter media unless something like a polishing pad is used. Even then it may not work. Time almost always takes care of bacterial blooms.