What is this?

[Rodolfo Garcia]

I have been battling with this brown stuff on my sandbed for several weeks now. It seems to subside just a bit when lights are off but never truly goes away 100%. Im in the middle of a blackout for 2-3 days and i can see it on the sandbed still. I bought a microscope and took a sample and this is what i saw. Any ideas? Im not sure if these are dinos or diatoms.

 

[Rodolfo Garcia]

I should mention my Nitrates are at 8.3 and phosphates at 0.07.
I use distilled water from a local grocery store called HEB. I’m wondering if the water there has silica.

 

[Rie]

I mainly see dinoflagellates and diatoms.

 

[Rodolfo Garcia]

I mainly see dinoflagellates and diatoms.

Do you know what kind of dinoflagellate?

 

[EnterName]

A = Diatom
B = Diatom
C = Dinoflagellate (I can't identify the species, the chromatic aberration is making the image too blurry but from the movement alone it's more likely Prorocentrum or Amphidinium than Ostreopsis).

The Dinoflagellate is a non-issue here. They prey on diatoms and it is normal to see a few amongst them. If they take over the yellow/brown stains become very slimy and start to form bubbles.

If the tank is just a few months old a diatom phase is normal even if there isn't too much silica in the water. However, if you are already past the ugly phase I would double check the water you are using. I have heard many stories of distilled water or RO/DI from a fish store not being properly deionized and containing silica.

You can find a few images of dinoflagellates and diatoms in my microscopy thread if you are interested.