if not fed, the flesh will recede until it dies lor.. showing only skeleton lor..
dun worry man, suns are very hardy, if u feed it often, it will grow back and be fleshy in no time..
it is normal for suns to open only at night.. maybe for a start, u feed them at night lor.. even better, no fishes to kajiao..
whenever i feed my fishes, the suns will all bloom big big, even in the day.. u can try frozen cyclopeeze.. one squirt, all will open.. the smell drives them crazy..