just got 4 green chromis a few days ago. the first day they ate and schooled around without a problem. as of today, three have been schooling and the fourth just hangs out in the same spot of rock and won't eat or leave that spot. what can i do? i know the others aren't picking on him...he's been watched. no visible signs of sickness are evident. his color looks good as do his eyes, and his breathing is normal. he ate the first day, but now refuses. what can i do?