I've been using Espoma sulfate of potash in my tanks for 2 years. I've had no problems like Ivo had in his pond. It is a little dusty but it's gone in an hour. I still have 2-3 years left inthat bag. Tom Connors, Pittsburgh Pa. I wish I could be half the person our dog "Jed" thinks I am! www.printsandportraits.com