Star- I'm going to go ahead and respond here instead of on the wall, it will make it easier to communicate and share, etc. :)
He's a nice looking boy..
Look for white specs on him, similar to grains of salt.. or wiggly worm-like objects on his body.
When he goes to the bathroom, is his waste brown-red or white and stringy?
The lump looks like it may be lymphocystis, which if that is the case then all you can do is keep the water clean until it runs it's course. If it "pops" then you will need to do a large water change to avoid infections. If it is lymph, then there is no treatment for it, just keep up with regular water changes, possibly even adding another small one depending upon size of tank, water change schedule. In time it will go away on it's own.
It may also be a tumor, and that there is no treatment for it other then clean water...
Now, you say darting.. does it seem as if he is trying to scratch himself on things.. or is he sitting still then takes off for a split second then stops right away?
Or is he swimming up and down, all over quickly?