It's most likely because of their diet. Both CBB and MI are very specific about what they eat in the wild. Therefore their digest systems are adapted to what they eat. If you feed some foods that not their nature diet, they may eat them. But they probably won't be able to digest them. Or maybe they can digest the food, but there are some specific nutrients in their diet that are missing from what they are eating in our tanks. This specifically apply to MI since we know that their main diet is sponge in the wild.

this fish is hilarious and so interesting to watch.

when i feed the tank i always feed it on the left side and allow the powerheads to scatter the food.

well he figured it out so when he sees that im feeding he goes up to the egg crate and puts his mouth through one of the holes so he can reach the food before it crosses the eggcrate

George has the right idea. Most Butterflyfish, some Angels, Moorish Idols, some other fish...they have poor long-term survival. The cause hasn't been studied (as most things in the reef hobby), so it is not known for sure, but the pros are suggesting that it is likely due to us being unable to provide a suitable diet for them to thrive long-term. Most of these fish naturally eat a lot of sponge in their diet, but again that hasn't been studied so there could be other things we are missing. Your best bet is to feed a specie intended diet.

moorish idol still doing great.

eats everything i feed my tank (nori, NLS, Formula1, brine shrimp, plankton) plus ive been using sponge power and theres hundreds of pineapple sponges growing everywhere and he hunts for those throughout the day.

Marko good to hear man , put a mirror in front of the tangs and that will solve your problems i did it for 2 weeks and now its like they dont care m y kole is constantly looking for himself too funny

Thank you...

I just sell them if they mistreat my moorish idol

Have you taken out the eggcrate yet?

Such a beauty I wish I could find a store willing to QT for that long. I would buy one too.

Yeah I took it out 10 days after adding the fish

I hate you right now.. Man those are nice fish.