Dinoflagellates, diatoms, cyano?

[jvfarrell]

So I’m dealing with a big problem in my tank with rust colored covering on the sand and some glass. Tried a filter test i saw mentioned on a post from this forum from years ago and my results do not seem completely aligned with expected results. I siphoned the material and some water into a bottle and vigorously shook it for about a minute. The siphoned material did not completely dissolve. A lot of it was captured in a paper towel filter as I poured the water into a clear glass. The water in the bottle was brown, but pretty clear after going through the filter. However, it started to recolonize in the glass after about 45 minutes. The recolonization leads me to believe dino, but surprised it did not dissolve more and was captured on paper towel. In addition, my water is not as pristine as i would expect for dinos with my nitrates around 12. Thoughts?

 

[Tuan’s Reef]

looks like cyano to me