can anybody help me figure this out i purchased a yellow parrot fish about 3 weeks ago and recently it has developed black marks on this fins and body but has no signs of illness.i also purchased a blue parrot fish 2 days ago and it rarely swims around it just seems to lie against the filter with its head looking up at the top of the tank.the yellow 1 also keeps nipping at the blue 1 and thats the only time it moves. if any1 can help i would really appreciate it