Has your tank ran at 81F all year? Do you get temperature swings? I had to buy a chiller cause I couldn't temp steady in my tank. Has your alk always been that high? Your LPS and softies might prefer a lower alk. Be careful with large water changes while you're switching salts. That IO could drop your parameters too quickly, particularly alk. I think you are on the right track with allowing the parameters to slowly go down to the Instant Ocean levels
Is there sunlight hitting the affected side of the tank?
Might tank has always been 81-82°, no fluctuations but a little higher than I would like. Don't think I have room or $ for a chiller. no sunlight hitting the tank. The affected side is the "bad boy"corner, where I've kept hammer, torch, frog spawn, Kenya tree tucked in the back. No sunlight.

