Black algae on surface of sand

[Scottmac]

Hello,

My tank has been set up for a few months now and I am going though the ugly phase (ugh.. when will it end???) I thought I had dino on my sand so I got anti-silicate pouches and made sure all the sand was thoroughly washed. But its not going away and I am starting to think maybe its something else as dino tends to be brownish but this is black. Can you please advise what this is?

I last cleaned the sand 2 days ago, now it looks like this again (this is under white light btw so that's the actual colour):

 

[sixty_reefer]

It looks like Cyanobacteria, what are your parameters?

 

[taricha]

silica sand?
If so, I certainly wouldn't try to remove silica from water with products. It'll be pretty expensive and ineffective.
Interested to see what those brown things are. would love to see microscope shot.

 

[Scottmac]

Phosphates are high, nitrates between 20-30. I will try replacing the white coral sand with black Hawai sand, but if problems like this keep coming up I am tempted in going back to freshwater as it's really not worth it and the tank looks ugly as sin.