If you happen to be using seachems purigen, make sure you are using a compatibale stress coat or you could cause a reaction that would make it inhospitable for your fish. Check out seachems website and their FAQ on purigen. If you are not using it. I don't and have had no problems with my fish, I use RODI, do weekly water changes and moniter my water quality and all there food are supplemented with vitamins. I use to have issues with Ick until I started using the the Vitamins.