Did you save the parasite do you have a picture of it? Fwiw, to me it looked like some sort of flat worm have you introduced and new fish or lr lately? I'd be concerned where there's one there's more. I'd also consider starting a q.t. tank if your still stocking your tank or tanks. It's easy if your doing tanks for smaller fish just set up a 20 gal with no substrate, pvc tubes for hiding, and a sponge filter. Keep the sponge in your main tank hidden in your reef so it's ready to go.
If you do have a parasite it's true that a fresh water dip is really a good way to get rid of invertabrate external parasites. Just dip the fish in warm fresh water for about 1.5 to 2 mins. Inverts are much more sensative to ossmotic shock than any of the fish. You might have to dip once or twice but, in many cases it's the only alternative,"glad that wasn't the case here."
hth