i moved some sand back of the tank to the front as it was been blown over the place this was about 4 weeks ago was fine till then tank has been running 7 months
Probably that stirred up some nutrients/detritus and/or buried some organics that then decayed.
It will probably go away on its own, but creatures that turn over the sand at least make it look nicer, if not actually getting rid of the diatoms or whatever it is.
If it doesn't go away, I'd look to reduce phosphate in any of a variety of ways or, specifically for diatoms, reduce silicate with a media that binds it.
Had a new setup on a 75 gallon. Big diatom bloom from all the silicates in new sand and dry base. Super good for cycling tank and everyone is right. Grab some reg leg or blue crabs and snails. Dont miss out on this opportunity to start your cleanup crew. I have about 30 each and its spotless showroom style