How do you know what disease a fish has He cluster of white bumps that now look like they are falling off another area was the same and it turned black one bump on heand?

White bumps falling off: These symptoms could indicate a parasitic infection, such as ichthyophthirius multifiliis (Ich) or cryptocaryon irritans (marine ich). Both parasites cause small, white bumps to appear on the fish's body and gills, which may fall off after a few days. This is known as the "saltwater ick".

Black bump on the head: A single black bump on the fish's head could indicate a bacterial infection, such as columnaris disease ( Flexibacter columnaris). Columnaris causes skin lesions that can appear as black or red patches. The lesions may also be ulcerated and may spread quickly.

To confirm the exact cause of the symptoms, it is best to consult with a veterinarian or an experienced aquarist who can examine the fish and recommend appropriate treatment.