These parasites are visible on your fish. They look like clear scales which undulate and sometimes flip up away from the skin or eyes of fish. Their presence often goes unnoticed until lesions or cloudiness develop externally. Most commonly you find the flat worm Neobenedenia mellini on the eyes and/or behind the pectoral fins of larger fish like angels and tangs. This worm lays eggs which hatch between 4 and 10 days and so if you treat with a bath, it's important to maintain therapeutic levels of meds long enough to kill the babies as they come out of the resistant eggs. Formalin (1ml/10g), copper (.2 ppm), or praziquantel (2ppm) but a freshwater dip is usually enough to knock the parasites from fish and the eggs are environmental and won't stick to the fish being transfered.