how can i clean the sand??

[anemoneguy]

its been a long time since i set up a new tank. let alone a 180. i had things looking good and then i lost a good amount of water due to a plumbing leak. well since then i have had my sand and rock covered with ugly brown algae. i thought i had a phosphate problem and was told to try knops po4 eliminator. its a liquid. and that po was hard to detect. so one dose and its seems worse.all the other parameters are fine. i even bought a canister filter to help clean things up. i spend time blowing off the rocks and changing filters. this is getting better, but now to my real question...can i use a gravel vac on the top layer of sand, or will it not work right being small grains of sand and not gravel? please if anyone has done this lmk, i will go get a vac, but just didnt want to waste any money. thanks