So my tin is out the roof and I have nothing rusting in my tank or any signs of rust. I dose with a kalkwasser for an auto top off. It's not a BRS kalkwasser just a garden variety I bought at walmart. Have used it for years in my previous tanks and never had problems. So don't know if that is my source or not. My other sources could come from some man-made rock that I have had in the tank since I purchased it. Or I went to Lowe's and made my own screen cover using the what I believe is aluminum frame and the plastic mesh to stop the fish from jumping out. my question is what can I use to safely remove tin from my display? I am running a poly filter and that does not seem to be pulling the tin out. Should I use puregen or Cuprisorb?