Juvenile with fungal infection

I rescued a little baby Axie from a garden centre the weekend before last. he is only about 3 inches in length and is very thin. He has lost the end of his tail and he only has stumps, rather than legs at the moment, so he's been named Stumpy. He has been eating very well since we got him home (blood worms) and his tail has started growing back, and he is generally quite active.
I am keeping him in a large plastic tub at the moment as he is too small to go in my axie tank, and i am changing the water every day. The water is prepared at least the day before and is stored in the same area as the tub to keep the temperature consistant during water changes (20-21 deg). I use a dechlorinater to treat the water, nothing else.

I've just got in from work this evening and noticed that he has started to develop a white fungas on his gills (fluffy, slightly translutant). I've had this before with my older axie, and the condition was treated sucessfuly with salt water baths. However I was convinced that with my older guy the condition was caused by water quality as his tank was cycling at the time.

Right! Questions!

1) What do you think could be the causes of stumpy's infection?

2) Am i OK to salt bath a baby? poor little man.

3) If i can, what sort of salt to water mix should i use, i haven't done it for ages.

Any help or advice is, as always, much appreciated.

Heya, I'm not an expert but do you reckon that the fungus could be from the stress of constant water changes? I would suggest you put him in a separate tank with a filter so the tank that he is in has a proper bacterial cycle. I think if I was in your situation I would get him into a stable tank set up before I began to salt bath to reduce stress, but thats just me. I'm sure it would be ok. Also try to feed him earthworms instead of blood worms as they are more beneficial for your axie especially if he needs to regenerate limbs poor lil thing I hope he does ok x