50% waterchange immediately and throw that bottle of Coppersafe away. The words Copper and Safe do not belong together. CopperSafe will kill any plants or inverts in your tank. The level between external parasite treatment and copper toxicity is very slim.
Im not giving you this advise for you to do what you like with it. Hex will kill a fish if not treated correctly. You are not even treating for remotely the right problem and putting yours fish health at risk even more. Why are you asking for advice, then doing the opposite to potential kill your flowerhorn? Dont let your girlfriend kill your fish.
*If CopperSafe is used with any kind of water treatment to remove heavy metals. The metal removers will break down the CopperSafe and it creates some sort of toxic coppery byproduct that most likely will kill all fish. Coppersafe is one of the worst products on the market IMO.