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You can just wait it out. They'll take over your tank for a couple months, you'll consider throwing it out the window...then they vanish within a few days. You can clean off decorations and stuff if you'd like...but they'll just keep coming back until they burn themselves out. I think almost all of us have dealt with a diatom outbreak in newer tanks.
I've had the same exact thing on my white gravel. It makes it look like I don't clean my tank. My BN Pleco doesn't touch it either, so I guess it will be here to stay for awhile.