How big a tank? What kind of sand?
I just got done doing what you're considering. After getting out everything but the sand & water I drained about 40% of the water into holding tubs (where the LR
& critters were kept). I left the filter running (Fluval 305 canister) and stirred the heck out of the sand. With all the gunk still suspended I siphoned out 5G worth, then replaced it with 5G of salt water made from dechlorinated tap. Repeat. Stir stir stir, siphon, replace, repeat. 3 5G buckets worth. Then stirred some more and pushed all the sand to one side so I had bare glass in one corner. Siphoned off all the remaining water. Refill with RO
mix & the old water from the holding tubs.
I noticed that the cloudiness stirred up while refilling seemed to fade away a lot faster than the first time we filled it.