Diatoms

Hi everybody. I have a well established tank. It is about 10 years old. I am having a terrible diatom problem. I do water changes, stir the sand, cut back lighting, added phosphate remover, charcoal. Seems like I have tried everything and no matter what I do the brown stuff covers my sand. It has been like this for months. Any further help would be greatly appreciated.

Thanks,

David