I have 5 red blood parrot fish. They seems very active, healthy and keeps on swimming 24 hours. I have kept them in 6 foot long, 1.5 foot wide and 2 foot height aquarium. Two of them have very little black patch on their body. Its just looks like nature color. But somewhere in net I heard about black spot disease for parrot fish. What is this black spot disease? Is my parrot fish also suffering from this disease? If they are then what to cure this disease? I am keeping them from long. They have got black patch when i bought them.