Thanks to you both for the fast suggestions! Until this week I hadn't heard about the EI system so I was trying to do a homemade version of the Sears-Conlin PO4 limited method. I had gotten to the point where my Fe was between 0.25 and 0.5 and my No3 was finally over 10 ppm. I thought the problem might be low K levels so I ran across Greg Watson searching for K2SO4 sources and he directed my to the EI system. I plan to start it up this weekend...

My tank is 15"D x 20"H x 36"L (listed as 50g, but that’s actually closer to 47g). I turned off one PC bulb so I should be closer to 2-2.25 now.

I'll try adding some more of my K / Fe supplement. I had read that going much about 0.5 mg/L is bad, but then again, I have lots of Barr Report back issues to read through this weekend. BTW, I'm using Nutrafin Fe test kit by Hagen. My only data point so far is that it say my tap (or should I say liquid rock...) is close enough to zero that I seen no color change. At this point about the best I can say is that I definitely have more than none and may have 0.25 to 0.5 mg/L.

Tom

PS. I meant to say the green fuzz is 2-3mm not cm.