Bummer. Sorry for your loss.
When you say that the parameters are "good", what are the exact parameters? How do you test? Has it been eating well? What else is in the tank?
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8G Peacock Gudgeon, 75G CA/SA cichlids, 120G Planted, 50G Mixed Reef (
Build). 125G Reef and 100G frag tank in process.
Save the reefs... Buy captive raised when possible!