How long has the tank been setup? This isn't uncommon during the ugly phase of a new tank. How long do you have white lights on in the tank? You may want to cut back the lighting and the feeding (or increase water changes/filtration).
Basically what peace said earlier^.
Algae in the sand bed is pretty common, you could always get a conch to help you out with that too. Also ensure lights aren’t running for too long, if you don’t need the high light then don’t run it. All it will do is feed algae