My tank is 75Gal - 2 pj cardinals and 2 cardinal - rock blenny a few shrimp and emerald cabs and a watchman. Tank has been running problem free for at least the last 18 months. Suddenly one of the pj's has a clear boil on his chin. No other fish appear affected. My worry is as the boil grows it may rupture which I am sure will kill the PJ but I don't know what the material exposed will do to the rest of the tank. Any thoughts on what it might be and what could be the cause. Thank you in advance for any insight and advice. CM