I haven't the foggiest as to how to cause it correctly. ;-)
Sounds like fish thyroid (benign tumor) problem. Untergasser (_Handbook of
Fish Diseases_, TFH) treats it with iodine and potassium iodide. Takes 2-4
weeks to slowly start to regress.
Stock solution: 0.5g iodine and 5g potassium iodide in 100ml of water.
Use 1cc of stock solution to each 50 liters of aquarium (and change) water.
No charcoal filtration, but do in the regular tank.
I'm always amused when folks get anal about the iodide trace in table salt,
when compared to the above treatment. <VBG>
Wright
-- Wright Huntley, Fremont CA, USA, 510 494-8679 huntley1 at home.comIn retrospect it becomes clear that hindsight is definitely overrated.