So I can still salvage the rocks
No, he's saying the rocks will leech out copper because they've absorbed it. To be candid here man, I would say chalk it up to an expensive mistake, replace the sand and the rock asap... Here's how I would do it:
Buy OceanDirect Live Sand from CaribSea, not the "AragAlive" nonsense. They make 2 grades of this, original which is unsifted sand harvested from the ocean floor, and the Oolite which is sifted so that you only get basically sugar-sized sand particles. Get whichever you prefer, but keep in mind, if you have decent power heads, you may have to turn them down a bit due to how shallow the tank is, if you go with the Oolite.
Buy the CaribSea Moani live rock, and maybe some of the South Seas shelf if you want the rock to rest firmly against the bottom of the glass.
All three of the above products are available at saltwateraquarium.com, I am not sure if BRS carries the Moani rock, I don't recall ever seeing it there before.
Buy a bottle of Fritz bacteria.
Once the stuff arrives, transfer your Shrimp and inverts to a 5 gallon bucket, transfer your fish to the QT, drain the display and dismount any of your coral. Give the coral a quick rinse under some RODI water, and place them in the bucket with your shrimp and inverts.
Drain the tank, chuck the sand and the rock somewhere.
Re-scape, add new sand, and fill with fresh saltwater. Add your bacteria. Wash your pumps and other equipment with some citric acid, place it all back in the tank, and let the water get to temp. Slowly acclimate your CUC back to the tank, while leaving your fish in QT and remount your coral to the new scape.
The bacteria from the sand, the spored bacteria from the rock, and the bottled bacteria should give you enough of a biological filter that the shrimp, snails, and hermits should be fine. Toss some food in there for the crabs and shrimp every couple/few days.
Once the quarantine is done, go ahead and move your fish back to the Main tank, you won't have to run a 6-8 week fallow period to get rid of the velvet because you've already replaced everything.
This is how I would handle it personally... I know you've already invested a bunch of money and lost some expensive things. I'm just trying to help you avoid making further mistakes.