Black ich, black spot desease or tang desease,its all the same.

If you have seen this around,its not a form of ich,as in the protist white spot!

This is not a protist,it is a a worm species that exists at its best in a dirty tank environment and as with other pests, needs the host fish’s immune system to be compromised by stress.

They normally only have a go at small-scaled fish like tangs-surgeons on average.

They live in and eat detritus until mature, keep your tank clean, free of any substrate and they are of no concern!