Illness/Sickness: Axolotl sick. Disease or bacteria? Photo attached

So I wake up and see that my Axolotls are not looking very well at all. This photo is my male axolotl and he seems to be the sickest. He was sharing a 4 ft tank with my other females. I can't understand what's actually happened as I change 1/3 of the water weekly and there is never any food left as I only feed them two/three times a week and everything gets eaten. Maybe it was stress but from what as they are never exposed to light and the filters are not huge and there isn't much of an current of water and the air sponge I have in I thought they likes as that's where they'd spend much of there time. I have lots of artificial plants and plenty of hides for them and the water temp was always between 16-19•c and they have been eating frozen blood worm and earth worm. Any way I put them all in quarantine and separated them all into individual tubs and have kept them in the fridge. I have soaked them in a salt bath once and going to do this every 24 hours for ten minutes per soak (2 tea spoons salt per litre water)
My questions are:
1, Am I doing the right thing buy salt soaking them and then housing them in the fridge?
2, if so should I not reintroduce them till they are all better?
3, what could of caused this to happen?
4, should I amputate the rotten legs to remove the infected parts?
5, should they be fed whilst kept in the fridge? If so how much/often?

Thanks for your time.

It looks like he has possibly been bitten by one of his tank mates. I personally would not salt bath them unless you see cotton wool like fungus on the wounds, tea baths or Indian almond leaves may be more gentle Caudata Culture Articles - Illness Part 2. You could keep him in the fridge, but he may be better off in just a cooler room. Make sure he is kept in cool clean water to reduce risks of infection. Offer food, but make sure you remove any uneaten.

Thanks to Julia for that fab info!

As for re-introducing them...if it really is a bite from a tankmate it may be better to house the injured axie in another tank, if you can. I know tanks aren't cheap but it may happen again. Maybe the females object to the male in their tank, even if they haven't minded previously? It's just odd that they haven't had an issue up to now. By the sounds of it it's unlikely he's snagged himself on a hide or plant, as I can see what appears to be a bone in the foot. Their skin is very delicate, but it would still take a bit of force to tear that skin off. Could he have got it caught somewhere? Is there a tight spot he may have got caught in? Did he get too close to the filter? If it is merely something in the tank (which is in no way your fault, axxies can and do have accidents in otherwise completely safe tanks) then he will probably be fine going back with the females. If they have bitten him, the fear is that they may bite him again. I only assume it must be another axxie if he was bitten because you didn't mention any feeder fish or other tankmates. I'm afraid that not being there personally I can't tell you which it is, and it is ultimately up to you to decide what caused it and what to do about it. I would recommend having a small tank ready just in case it is another tankmate attacking him.

I wish I could tell you for definite, but all I can offer is opinions and advice. As for amputating the limb, I didn't know you could do that. I would probably suggest no, but I am not a vet and have only had my own axxie for a very short time (all of my advice is either from sites or from limited personal experience). There is a chance that given plenty of clean water which is filtered or changed regularly and enough food, he will heal himself (it takes around a month to heal damaged gills, not sure about feet). Like Julia said, keeping the water clean and 'fishing' for poop and food after is the best way to stop infection, and of course, there are the tea baths she suggested. I can also suggest a feeding jar, which I have found massively effective in helping to keep the tank clean as all waste is kept in the jar, preventing cloudy water.

Good luck! I hope he is better soon!