Dinos? Algae?

[Multra]

Hey, my tank is 70 gallon display/30 gallon sump about 6 months old at this point. Bare bottom w/ Chaeto for nutrient export and carbon in a bag. I have this fluffy or cloud like brown/green stuff on my rocks, not sure what it is. Got some pictures of it under the scope at 1000x, the cells are not moving at all so I am guessing it is some sort of algae? Snails and the urchins seem to eat it a bit and haven't died.
0-.05 phosphate
0-5 nitrate (was stuck at 0, started dosing potassium nitrate to get it up, seems to eat about 1ppm/day)
10.2 DKH
453 CA
1270 Mag
8-8.1 PH

I used to do a 1.5 gallon AWC daily but I stopped that 3 weeks ago since my nitrates were stuck at 0. I have started dosing K-Z Sea Water Complex, Acropower, and Vibrant. Been dosing the Vibrant for about 2 weeks and haven't seen a change to this stuff. Any idea what it could be?

Thanks

 

[saltyhog]

That looks like chysophytes to me. Interested to see what the experts say.