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.

Don't worry about starting a mini cycle if you put in new carbon. As long as you don't change your filter pad and/or biological filtration media in the filter at the same time, you'll be fine. The only real function of carbon is pulling nasty chemicals out of the water, so changing it won't start a cycle. Carbon definitely needs to be replaced often; about once a month or more frequently than that. The reason you need to change it so often is that carbon can only pull so many chemicals out of the water; after it reaches this maximum absorption point, it can start leaching compounds back into your tank which isn't good for water quality. Leave the carbon out of your filter until you're done treating the tank and then put new carbon in to get the medicine out of the water again. After your fish are better, I'd recommend getting a new filter. One of the best brands is AquaClear. Really reliable, quiet, and reasonably priced. Definitely get one of those. And when you switch over to the new filter, leave some or most of the old filter media in the tank (or in the new filter if there's room) to make sure that you don't lose any of your biological filtration. Good luck and let us know how things go

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When in doubt, do a water change.

the carbon filter i am using is the aqua tech ez change....so i can change out that and not effect a cycle? i always thought that my bacteria was in that filter and the other filter element (a more coarse one) was for bigger stuff....after a year im still a newb!

The course filter thing is for growing bacteria colonies bio filtering, the fine filter is for mechanical cleaning, floating bits, and the carbon is chemical, ammonia and such.

ok awesome! thanks....i feel like an idiot! as soon as i get this disease stuff gone ill slap a new filter in. thanks a bunch guys and gals!