I have used sugar, and I know guys are going to think I am crazy. This was one my 29G with 20G sump. The sand bed in my Display was 3", sump was 5" or so. NA:0, NI:0, A:0, PO, 2-5PPM (!!!). The PO3/4 levels I attribute to tap water I used in the beginning. Now I use RO water only.
So I tryed it. After the MAJOR HUGE bloom, all zeros, except my phosphates were at .5PPM and steady. I did lose a Clown, and Chromis. When it bloomed, it looked like semen, no joke. It was bad! But after wards, all was well in my tank. It took a week or so to clear up.
.5 May seem high to you guys. But Organic PO are required for life, and new growth of EVERYTHING.
I still have some hair algae growing, and thats fine. Its a good food source for my blenny, and probably a tang or two.
Bottom line is, it works. Its crazy I know. But it does work, and the algae is under control now. It took a major shock to my system to get it under wraps. And it does create a "monobloom" which will work its way out in the end.
I never told anyone I did this. Because people think its crazy. But chemically, and biologically its sound. It works, and it makes sense. I don't think you should try it. Unless you understand the chemistry, and know your system. In most cases its not needed. But if you fall into that group, who has a build up, thats not controllable. Well then, thats up to you. In my case, it worked, and very well to bring things into line.