I got a moorish idol yesterday.
I studied alot on them, Read alot of articles and books because i want to try get this right.
The idol does have a diet of sponges and some say water is a big factor in there survival as well, Some people that have kept Idols long-term do 100% water change each day (Those that live on the beach having auto water changing machines)
And ive also read, It depends on how the idol was caught. and they're transport. Make sure the Idol is caught by net, No chemicals helping them. And when the LFS order you one in. Make sure his eating.
The one i got has been nibbling on mussle and alittle nori. Hasnt had a full go at it yet, But nipping. It is a start.
I will keep you updated on how he goes in the tank, Lovely fish but will need to be kept with alot of care and attention.