Canister, remove the bioballs and add more live rock rubble. Bioballs end up being a nitrate factory. By ocean rock, do you mean rock you picked up from the ocean? Can you send pictures?
Your main question can you take everything out and put new sand and water? I really need to know more about this ocean rock. If you had enough LR
you could do something similar to what you're talking about because the good bacteria is in the LR
. I think with what you propose you're still going to have a cycle and you don't want to put the fish through that. Still concerned with that regal, how big is the fish?