Is this mold?

[Katy]

Hi, I’m new to the forum, but not to aquarium keeping. My betta passed away about a month ago and I cleaned out the tank and got it ready to set up a new aquarium. It will be for another betta with a heater and a sponge filter. Decided to try a dirt tank for the first time with a black sand to cap it. All live plants and I’m wanting to add some snails once the tank is ready. No ammonia, only .50ppm nitrites left and 10-20 nitrates. Recently I’ve noticed this white stuff at the bottom of the tank. I’m concerned that it’s mold but I’m not sure, could anyone give me some more information? 

[Odd Duck]

Looks like biofilm.  Usually clears with time.  Siphon excess out as needed with water changes.  It typically clears quickly once there are snails/fish in the tank since they either eat it or stir it up and dissipate it.