I have 3 tiger barbs a red tailed shark a clown knife fish a Cory cat fish a plecostimus and a loach that looks like an eel (not sure of technical name), anyways they're in a 38gallon tank and the barbs have black spots and what looks like fun rot. The plecostimus and red tailed shark look like they have it too. I have 2 large plants in the tank. What should I do I just did a water change 15 out of the 38 gallons.