Agree, you have to get it out quick.
Recommend that you
1) Syphon out what you can get without digging in too deeply into the sand.
2) Do a PWC
(2 this week if you can) with RO
3) Point a powerhead in that general direction to increase the flow
4) Cut back your feeding to once every other day
5) Cut your light cycle to b/w 6 - 8 hrs (until you get it licked)
6) look at your setup and see if you have any possible source of nitrates or phosphates, like sponge media in filters, bio-balls, HOB
filters that can accumulate the waste and uneaten food. ( I would get rid of all the external media and replace with LR
7) Check your water source to see if that is putting extra NO3
or phosphates into your tank. Remember, even if you treat tap water with Prime, those "inactivated" chloramines will eventually turn into NO3