See that's just it. I'm not 100% sure it is Diatoms. It acts more like Cyano. Goes away at lights out and gets worse the longer lights are on, glues sand together.
At least if this doesn't work! I can rule Cyano out. I've ordered a Media Reactor so I can run a Silicate remover of some type.
Either way I'm getting rid of this crap if I have to remove the entire SB-lol.