Just curious, what if I were to keep the mirror in the tank 24/7. Would it stress the fish out too much and lower immune system or something?As long as it's a mirror he can see himself in it doesn't matter how big or small it is. It's just the act of chasing off an "intruder" that helps with color development and kok growth. Now this part is the important part. Only use the mirror for 15-20 mins (After) feeding. Never do it before feeding otherwise they may refuse to eat because they're all pissy still. This method also work for females as well, you just see as much kok growth if any at all.
Another part of grooming I do too is more or less live treats every now and then. This is more for personality then anything else. It's also good for jump starting the breeding process.