I like Salifert phosphate test kits Otty, 12-14.95 anywhere online...easy to do, fairly easy to read. If you havent tested before for PO4, I bet it's off the scale then..but Im guessing. I've always had PO4 troubles...
prob just nuisance algea thats feeding on the PO4 and NO3s....
I have to clean my glass everyday too. And my sand is always brown...
I ordered mangroves off Ebay , 25 for $22 delivered, and hope that helps me out. I also have a 29g tank Im making into a sump/fuge, as soon as I can get some plexiglass to make the baffles.
More clean up crew maybe??
good luck
Scoffer