Dino, Cyano or Diatoms ? Please help !

[DarkTonio]

Hello,
Tank is 50g - 5 months old - 0.00 PO4 and 3.0 NO3
I have this brownish dusty stuff growing on my sand. It is visible during light time and disapears at night (?!).
First, I thought it was dino because I know I have been far too low in PO4 because of Rowaphos in a reactor running 24/7 for two weeks (big mistake). I am trying to increase both nutrients (N&P) right now to be slightly above 0.
So, I said I thought it was Dinos but after looking under microscope I am not so sure anymore... I would like to know in order to have the best strategy to cure. I am asking for experienced reefers' help here because I am a newbie. Please take a look at pictures (I did the best I could). Thanks a lot in advance !

 

[vetteguy53081]

Appears to be diatoms
Siphon, reduce white light intensity and add a few snails such as cerith, nerite, astrea and trochus to help with control

 

[taricha]

one of the cells in this closeup is a dino, but it's mostly a normal early stage uglies mix.