Tiny round green balls - diatoms? Algae?

[ThunderGoose]

I've been having an outbreak of... something... for about 2 weeks now. If I stir up the sand it starts to re-appear within a few hours. Water changes to reduce nutrients aren't helping. Based on descriptions I thought if might be diatoms. I pulled out some sand and looked under my microscope and 1) my sand is swarming with pods 2) it consists of small, round green structures attached to the sand grains.

What does everyone think? and how do I get rid of or reduce it?

Thanks.

 

[ThunderGoose]

PS all the pods are green and about the same size as the mystery green stuff on the rocks. Maybe they're all the same thing?