Hi again Katie,
You should be able to take photos with anything (phone, camera, Ipad, etc). From there you only need to upload it online (at those sites I mentioned, even facebook, or attach it using the little paperclip icon on this page's task bar).
Anyway, if we have a fish that is now acting well in response to good water quality, this lump is not likely to be sinister (ie an abscess, parasitic cyst, etc). Instead, especially if he was under the stress of poor husbandry prior to now, I would be most suspicious that this mass is due to lymphocystis (a herpes virus). This virus causes mass type growths on the fish that will appear as soft tissue masses arising from the epidermal layer of the fish. There doesn't tend to be any irritation, ulceration, redness, or infection with these types of lesions. And really they tend to be more unpleasant for us to look at then being actually harmful the fish in itself.
Lymphocystis is actually becoming a more common finding in the domestic goldfish/koi world, mostly due to the ‘silent carrier’ nature of asymptomatic fish. The virus often infects these fish then lies latent, sometimes causing no disease in the carrier fish. Still we tend to see a problem with this virus when it does recrudesce and causes these viral induced masses to appear in the infected fish. This recrudesce is often linked to a weakness in their immune system (either because of their age, stress, if the fish is immunosuppressed or fighting some kind of infection that takes the attention of the immune system). And it is this time of weakness that triggers the herpes virus causes its mischief.
In regards ***** ***** to do with this lump, there is actually no treatment for this virus, and with time they can grow, become pedunculated and vulnerable to o trauma/infection. Furthmore, even though you have removed it before, we do have to consider that its recurrance in the same spot tells us that some cells were left behind last time (so that the original mass was able to regrow) and that if it is virally induced it can potentially come up again even with full excision (or even choose somewhere different to appear).
Overall, based on your description and history of his care at your boyfriend's house, this would be our top suspicion. Unfortunately, these lump's are not treatable but they often don't cause the fish much bother. Therefore, we would just want to let him live his life in this better environment and hopefully with your care he won't suffer further lump growth or develop other lumps due to the virus.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
All the best,