Help with brown sand

[Maho.B]

So I have been unable to stop my sand from getting "brown" and have read a bunch of threads and articles online, my best assumption is it's the variety of Dinoflagellate 'Amphidinium' given the characteristics I've read. This first appeared awhile ago, like 7-8 months ago, and at the time I thought it was maybe due to low nutrients as I was having a hard time keeping decent levels of Phosphate and Nitrate. In addition to regular fish feeding I started feeding daily with coral foods (rotifers, oyster feast and benepets) and it worked to get my nutrient levels up. All corals, except for one (forest fire Montipora digitata which I have no idea why) are doing great, all are growing and look great so I don't want to do anything drastic like a 3 day black out or any aggressive chemical treatment or anything to disrupt an otherwise healthy system. But I will admit I am not a fan of how the sand looks, is there anyone who has experience with this? It's not cyano or diatoms, it is fairly difficult to get off the grains of sand, and it almost goes "away" at night, then darkens as the day goes on. I have a goby, emerald crabs, conch, and snails that are constantly picking through the sand so I doubt it's toxic. Just thought I would ask if anyone found a way to get rid of it. By the way, the rock structures are nice and clean with coraline algae growing like mad, and the glass is clean, I get a light brown dusty like film that I use a magnetic scraper on every 2 or 3 days, so it's just the sand that is a problem. Thanks!

 

[EeyoreIsMySpiritAnimal]

Can you post a pic under white lights?

 

[EeyoreIsMySpiritAnimal]

Also, how did you determine it's not diatoms?

 

[Maho.B]

I will try and post a pic under white light shortly. I technically don't know it's not diatoms, but it doesn't wipe off the sand at all, it's like it is embedded in each sand grain. Also, the only water that goes in is RODI for salt mixing and distilled water for ATO. System is 1 year and 3 months old.

 

[Reefer911]

Might be crysophytes. I’ve been dealing with the same thing for a while

 

[Maho.B]

Ok here are a couple pics using the filter on my phone to cut out blues, looks weird this way, hope it helps! Crysophites? I'll have to look those up!