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IMO - I wouldn't add another fish for at least a month to make sure everything is good in the tank. It's not worth the risk to my fish and even though waiting is soooo hard ... it's for the fishes sake - not ours. I'd rather be safe than sorry.
Wait for at least two weeks after the last spot is gone. Then slowly start lowering the heat. I'd wait at least two weeks after that before adding any more fish.