Lumpy neons?

[darkmule27]

Several (maybe 3-5? of 11) of our neons have what I can best describe as bumps on their undersides. The others look perfectly fine. The lumpy ones have been lumpy without any changes for the past several days. They are all eating heartily, schooling happily, and swimming normally. They also all sleep at night, so no real restlessness.Parameters are fine...no ammonia, nitrates, nitrites, pH is around 7.6. It's a 20 gallon that has been set up for almost 8 years (convict cichlids for most of it). It's got an undergravel filter and some kind of emperor HOB fliter (the one for 30 gallon i think?).
The tetras range from about .75 inches to almost 1.5 inches. They were purchased in 2 batches, the first 5 on Dec 30 and the other 6 on Jan 2 or 3. We also have a BN who's about 3 inches and 3 platys (and possibly 1 hitchhiking platy fry, although I haven't seen it today). There are also a few live plants.
The water was changed yesterday, gravel vacuumed at the same time. Nothing new in there. The fish get a mix of freezedried bloodworms, dried "baby shrimp", betta flakes, cichlid flakes, floating cichlid pellets, veggies, and sinking algae wafers (obviously we're using up some leftovers).

So, what's the verdict? Is it Neon Tetra Disease? Is it something to just keep an eye on? Thanks for the help!