The rot looks like disease rather than bite damage so I would personally run 2000 again.

Just one of those things I suppose, but if he's happy, don't worry. Well done on raising them.

That's good to hear - hope he continues to improve.

The film on the air stone will just be biofilm - common in most tanks. Use 12 drops of 2000 for the extended dosage. You can use Exit at the same time as 2000, but he's not really showing symptoms of anything that would treat so it my be wise not to give him the additional stress of a second medication at this point.

It could be pus in which case the Esha 2000 should treat it. Most parasites are too small to be seen with the naked eye.

That looks like a (probably benign) tumour. There's no specific treatment for that. I doubt the bits in the water are related to it, probably coincidental.

No, just use the medication.

Use the standard 3-day dosage, and if there's no improvement continue for a further 3 dyas.

I've looked it up and it is toxic to fish so possibly, yes.

Treat him with Esha 2000 or Waterlife Myxazin, but be prepared for the worst as sadly, once they start to pinecone they often don't recover.