Powerhead help/ideas needed

[Glennrf38]

Hey everyone. I need some help with powerhead placement (I think). I have a 24 X 27 X 18 cube(ish) tank with a Seio 1500 and a 820 (I think. I can't remember if I got the 620 or 820).

My problem is that I can't seem to get all the dtrius out of the tank with them. If I go around with the turkey baster, my rocks are covered in a fine "dust" and I think this is causing my hair algae blooms.

I have moved the powerheads just about everywhere in the tank now and still can't seem to get the rocks or the bottom clean.

One LFS sugested adding another powerhead (Koralia 3 or 4).

Any sugestions????

Thanks