Personally I would leave that cat where it is, whatever damage has been done from osmotic shock, is already done. Whether it is domestic bred, or wild caught, makes no difference at this point. I'm an old fart too, and have seen thousands of imports of fish go from soft acidic water of the Amazon to tap water that is hard water with high pH values, with zero acclimation period, and zero issues. If you want to do something to help alleviate some of the osmotic shock (if this is still ongoing?) add a small pinch of salt to the tank water.
I would also lower the temp in this tank to 78F, 82 is a bit on the high side.