Around 2 weeks ago my 72 gallon reef tank which was flourishing up to that point,started showing signs of something very wrong, fish started to die and corals were closing up. I immediately transferred what livestock I could to another tank I had running and was able to save a couple of fish and 1 coral. Within 2-3 days, even the B-worms had come to the sand surface and died. I cleaned out what I could that was dead and did water changes. I had the water tested at a LFS and it seemed fine. They even tested it for copper and it was negative. LFS thought that something must have fallen in tank to poison it. I emptied the tank this weekend, stirred up the sand, and vacuumed as much of the yuck on top of the sand I could but found nothing strange. Cleaned out the filter, replaced heater with a new one in case it was damaged. I then put all new saltwater in it and replaced the live rock which was kept damp overnight in separate bins.
I am on the fence about if this tank needs to cycle again since I have all new salt water. While trying to get all of the yuck off the sand, I did use straight fresh water with some Prime to vacuum up.
Am I truly starting from scratch again?
Any help you could give me would be greatly appreciated.
Thanks.