Some kind of macro algae? Also looks like a light dusting of diatoms on the sand. Not sure what these are. Green, somewhat stringy, but they aren't GHA. These are less hair like (if that makes sense). It actually reminds me a bit of chaetomorpha. The color of diatoms, but looks more like some kind of turf algae. This is slowly dying off now. And a random one - hydrogen sulfide or just air bubbles? It doesn't look black like hydrogen sulfide normally is. The sand is also only about 1.5" deep.