In my 36 gallon tank I have an HOB MarineLand Penguin 200B filter with a biowheel. This specific filter is rated for 50 gallons. I have noticed that after going a while without changing the filter cartridge the wheel stops spinning. Im assuming this is because the build up of bacteria within the filter is minmizing the water flow. I dont want to put a brand new cartridge in because of all the good media building up in the current one. Has anyone else had this issue? Should I just replace the filter cartridge?