ok i have searched and as many of you know that only confuses you more. i have a 38gal aquarium...one of those walmart deals. of course im running that crappy walmart filter as well. at first i was having issues with cycleing...but now all is well..the tank has been running for almost a year now. well i never changed the filter after all my cycle issues. i would just clean it when i did a water change. my fish have some disease right now that im treating with pimafix and it says to remove activated carbon. my filter is an activated carbon filter. so i removed it and treated. now im looking around on the net and i see that activated carbon "goes bad" after so long....it just quits filtering effectively. so if i put a new activated carbon filter in am i gonna start a mini cycle? right now i have the old filter in a ziplock bag. i still have this brillo pad looking filter element in the filter tank to help filter stuff. i just dont wanna start a mini cycle. my fish are already sick and i dont wanna hurt them more. also i tested the water with an api master kit and ammonia is 0ppm, nitrite 0ppm, and nitrate 5ppm...ph was 6.4 and i just did a 25% water change yesterday before i started treatment with pimafix.