Should I remove my shallow sand bed - issues in tank

[Myka]

Fwiw, you can bring alkalinity down with Muriatic acid in your saltwater mixing tub if you want to. It doesn't affect any other parameters. Reducing nutrients via water changes is a slow and expensive process though.

What do you have for a skimmer? What do you use for filtration besides the skimmer? What are you using for powerheads? When yu do a water change, how does the procedure go? Do you simply remove old water and replace with new, or do you vacuum the sand (yes it's possible even with sugar sand, but it sucks) and blow off rocks? To me, it looks like a husbandry issue from the information you provided. Removing the sand bed won't solve husbandry problems, but it would quite likely give you a leap ahead of the problem, and would give you the option of using a coarser sand in the future that is easier to keep clean imo. Enough GFO would solve the PO4 issue, albeit GFO is expensive, and it won't touch the nitrate problem. Biopellets might be a good option for you to help you catch back up to "0", but imo, no tank should need to use biopellets forever.