Diatoms are algae that eat silicates to help build their “shell”. Without silicates, they’ll die. If you have no other livestock, why not give them lights to speed along the process? Silicates are part of sand, so your sand is actually feeding them. Once they consume all of the silicates in the sand, they’ll slowly disappear. This is part of cycling a tank. After that, you’ll want to make sure that what ever water you’re adding is free of any type of silica. Also, I can’t see from the pics, but you’ll want to find rock or some source of coralline algae. Besides it being beautiful, it helps to keep other types of algae at bay. But that’s another topic for later. Good luck.