There is a chance the Diatoms may never go away. They use silica in water to produce the shells that give them their brown color. If your PWC
source (tap I assume) has silica it's difficult to get rid of Diatoms. I've had them in my tank from the 2-3rd month in.
For now, just wipe them off. They come off easily and it wont fluctuate your parameters. They can burn off on their own as they use up silica which is common in new tanks, especially with silica sand substrate.
The link below has some info that can help.
Brown Diatom Algae Control | Aquariums Life
75g Planted Barbs Denison, BlackRuby, Tiger, Albino Tiger, Green Tiger, Cherry, Gold, Checkered, Odessa.
NonBarbs Cardinal, Neon, RummyNose, Bloodfin Tetras, Z. Danios. 1RTS. Amano, Bamboo, Ghost & RCS. 20g Long Shrimp Tank RCS, Tiger, Amano.