The only thing you should ever have to change is the chemical media and polishing pads (if you use either of them; neither of them are necessities). For the chemical media, it will say either on the box or on the instructions (or both) how often to change it, and for the polishing pads, I reuse them until they get clogged to the point where I can't squeeze the crap out of them anymore (pun intended ).Pazzoman;4572684; said:So one a month i have to change everything in my filter? Or should I change the first level of the filter one month, then next month second chamber, then third month third chamber and repeat?