Dino + diatom

[Happyjojj]

Hello fellow reefers,
Once again I'd like your help. I'm battling some thing(s)? and I'd like you to help me identify what exactly. It's this brown stuff that's 98% on my sandbed (rockwork almost completely clean of it) that just wouldn't go away. It doesn't matter how much I siphon it out it's always back. It's a bit better at night so I'm suspecting dinos, however I'm not sure about the microscope ID
Alk: 7.7
Mag: 1350
calc: 410
nitrate: 14
phosphate: 0.06
I attached some microscope pictures + a general look of the thing. One sample is from the glass other is from the sandbed. I can sort of make out some of the prorocentrum cells also the diatoms from the glass, however the rest I have no idea about.
Any ideas?

 

[Gumbies R Us]

Do you have a full tank shot?

How old is the tank?

CUC members?

 

[Happyjojj]

7 months
1 fighting conch
2 astrea + 1 turbo snail
4 nassarius
3 hermit crabs
1 peppermint shrimp
1 cleaner shrimp

load:
2 clown fish
1 goby

Before you pass judgement on coral placement, this is just how these jerks like it, the rhodactis literally climbed up there