Rough summer/concrete dust

[IanWR]

I must say if you are facing a total coral wipeout due to dust sized particles of unknown composition I don't see how any rock or sand could remain. For that matter, I would also redo the plumbing. Anything that I could not clean for certain would go.

I don't know how litigious you are, but you have experienced a loss due to the actions of others. If they were licensed contractors they should be carrying insurance that they may be able to use to cover damages. You should be compensated for rock, sand, plumbing, and possibly some amount for corals (no clue how that would get assessed).

Again sorry for you loss. Either you are apoplectic with frustration or you have the patience of Job.