Algae ID

[likwid]

I cant get rid of this stuff. I have tried adding PhosGuard to lower my phosphates, but that didnt help. I tried aiming a powerhead at the sand, but that didnt help. Tried cutting the hours of lighting, but that didn't help. I stir up the sand to get rid of it, and it comes back again within hours full force. Im getting very frustrated. I did a 50% water change using RO/DI water a few days ago and that hasn't helped eiter. I have no fish in my tank anymore, so I only feed my inverts a bit of food every 3-4 days, so its not from over feeding.