My friend and I both had it in our tanks he used chemicals and I didn't. He still has to treat his about once a month and I haven't had any return. We use the same water from my ro filter so I know it isn't that and use the same food. It is actually a bacteria and I think has a lot to do with in. On one forum they suggested when starting a new tank is to use tank water from a healthy tank during the cycle to help prevent it.