You know those bubbles you get on the tank walls after water changes? Those are little gas bubbles that come from . . . something, I can't remember and too lazy to look it up. But on rare occasions, those bubbles can get breathed in through the gills and cause bubbles under the skin, or gas bubble disease. Just want to make sure the Sparkster doesn't get that.
I wish I could pet him more. There's something so pettable about him.
Caused by gas saturation in water and is "amalgous to the 'bends' in human divers." It is mainly nitrogen gas that is toxic to fish above 104% saturation. "This condition may arise when cool and gas-rich water is quickly warmed." Basically, cool water heated by a heater. It also happens when "newly set up aquaria have been filled with cold tap water and quickly warmed to operating temperatures." Such as when we draw lukewarm water from our tap.
Source, A-Z of Tropical Fish Diseases and Health Problems by Burgess, Bailey, and Exell.