HELP!!! My two clownfish are acting very different. The tank has been cycled for years and all nitrogen associated compounds are at low levels. We recently had moved a new clownfish into the tank and suspect it may be the cause of these two fish struggling. Any ideas or solutions?

I ordered a product that is called “Kordon Rid-Ich” it is formalin based and contains something called malachite green. Are you familiar with it? If so would you recommend it?