Is it Phosguard? I use GFO and think it works great. I ran into the same situation once and couldn't get GFO. I bought Phosgaurd and I started getting a red algea in my sump and a little hair algea on my sand bed. Switched back to GFO and it was gone in 3 days. Could have been something else but I am sticking with GFO. I have also heard conflicting opinions about Phosguard leaching aluminum into the tank? May not be true so don't take my word for it!