Help with new glofish tetras

I just got three new glofish tetras. They are the only fish in my new (cycled) 20 gallon tank. Everything seemed fine on day one, but now after two days, I have some concerns. One of them barely swims around, won't eat, and has a white lump on its side. I'm worried he won't make it much longer. The other two are very active, but one constantly chases the other into the same corner and when he tries to swim out, he gets chased back in and nipped at. Do I need to do anything at this point? I wasn't sure if three would be enough but I didn't want to overload my new tank right off the bat. Any help would be appreciated!

Water conditions seem fine...No ammonia or nitrite and minimal nitrate. 78 degrees Fahrenheit, 8 gh, 3 kh, 7.4 ph.

Also, when I referred to a fish as "he" above, I really have no idea what sex any of them are...

 

I'm not sure about the lump, but it could be bloating. Cook a pea, remove the shell, cut it up and feed it to him.
The GloFish Tetras are GM Black Skirt Tetras, and are fin nippers when not kept in a large group. I recommend keeping at least 6 together, preferably 8-10.

 

Thanks for the reply. Would you recommend more fish? Whether they be glofish tetras, another type of tetra, or something else altogether? I don't want to stress them out, but I though I should start with a lower number and see how the bioload is.

 

How long have you had the current fish in the tank?

I would recommend adding at least 3 more of the same fish to the tank, since they are a schooling fish.

 

I've only had the first three for 2 days now.

 

They do need a group of atleast 4 to be happy. The lump... You could take the fish back to the store if they have a guarantee because it may be their fault. But these tetras are known not to live long.