The "feeding" the sand really means to help establish it with good bacteria
You may already know this, It doesn't matter if it is a 10g tank or a 300g, you have to have a full cycle before you add any fish, CUC or coral.
Get a mesh bag and put a piece of raw shrimp in it....that will kick start the cycle, once you get a good ammonia reading remove the shrimp ...use your test kits ...wait.... when the ammonia goes to 0 test for the nitrites, then when nitrites go to 0, test for the nitrates....do a nice water change, and retest for a few days to be sure no ammonia or nitrites are present and add that first fish.
There should be enough bacteria built up for fish #1, wait a month for the tank to balance and add fish #2. Using a quarantine tank will buy the time you need between adding fish. Going slow is the key for success in this hobby. Each new addition will add more ammonia, the bacteria has to be able to break down that new ammonia before it can hurt you live stock, so you must give the bacteria time to build up to handle the new addition before you add anything else.