Some people says it has some effect, but then on the other hand, everyone that has quit using it has experienced 0 problems or changes. I think this is significant. I don't use cycle, I use just a little dechlor, rince my filter media in siphoned out water rather than tap water, no carbon, and my tank has not changed, at all since when I first started, doing everything under the sun. Certain specific breeding situations or type of fish may require a specific water parameter, but most don't care. You can say it doesn't hurt, but as with cycle, I say carbon is the same. The one thing it does hurt is your wallet. Everyone should try not using it for a few months, see if you notice a difference. If not, then save yourself the cash. Once your tank is cycled, remember to keep it simple. Regular cleanings and water changes are what matter.