you can siphon the very top most layer of the sand, just to suck up the gunk, but stirring it up will just give me more ammonia most likely. An established tank should never have an ammonia reading, if it does then the bio filter is not powerful enough and you should invest in more live rock, a good skimmer if you do not have one. On my 46g bowfront I have 35lbs live rock, a small canister filter and an emperor 80 HOb filter to help out with the bio filtration.