It's called "new tank syndrone" or better said, uncycled biological filtration! Same thing happened half a year or so ago, if you'll remember, to another newly opened store in Toronto. About 20 years ago when Allan Soul (Al of bigals) opened his 2nd corporate store, they had a giant, newly set up, over stocked reef tank crash. "It was poisoned!" they said.

Ammonia poisoning!
The zoo and their sting rays! Pool was set up for a little less than 6 months and the pH kept crashing in that 6 months. How is a biological filter expected to become established in 6 months when the pH keeps crashing? Videos showed ammonia bubble on the surface of the water. New Tank Syndrone
Toronto's pH out of the tap is 7.2ish, not as bad as BCs <5 but it still needs to be continously buffered.
So here we have 4 guys who claim to be pros and have a "central system, which filters and heats 400 tanks holding more than 5,000 fish." included in this system are "hundreds of fish, including small sharks and rare shrimp" and "the store’s most expensive fish and 200 pieces of rare coral. Small bamboo sharks, lion fish and hundreds of rare shrimps were among the 700 exotic fish killed, along with endangered corals imported from Australia, Indonesia, Singapore and the Caribbean."
Please! These guys are newbs! What pro keeps sharks, hundreds of fish and corals in the same system? Especially a system that is only 6 months old?!
The bleach smell?
AMMONIA!!
Over night pH crash and that system failed.
That is what happened.