I know there are many kinds of filters out there that sound like something I should invest in. But for now here is my problem. Both of my tanks have filters that just hang over the back of the tank. One is a Dynaflo 1 and the other is a Aqua Regent. Where does my good bacteria remain when I change the filter cartridge? The cartridge is the only thing in there. Won't it be like a new cycle all the time after I change my filter? I did put a couple little sponge like things (they are more poreous than a household sponge) that I bought at the LFS in between my filter cartridge and where the water returns to the tank.