I just moved and found out that the water in my house is well water and it passes through a salt water softener...what would I need to do to make this safe for my axolotls? is it even possible to make it safe for them?
Is there a tap before the softener? I've read that salt-softened water isn't ideal for outdoor watering (lawn, garden, etc) so do your outdoor taps pull water from before the softener?
If your well water is pretty close to
Newmarket's municipal water, then based on my understanding, it's pretty much ideal out of the well at a KH of around 10 degrees of hardness and a GH of around 8.75 degrees of hardness. pH is a bit high at 8.1, but not really that far 'out of range.'
Since a sodium content above 200 mg/L is 'noticeable by taste,' it's unlikely that your softener inserts more than that. For what it's worth,
the salt solutions that people often add to their axolotl water add a substantial amount of sodium - John's Solution, for example, adds 1 gram per litre, which is 1,000 mg/L, which is likely over 5 times what's coming out of your softener.
But adding limestone to a water-softened tank is apparently a bad idea - as mentioned in
this article - so you would have to be rather thoughtful about what other items you add to the tank.
All that said, I'm not a chemist and I don't play one on TV, and despite having done tons of research, I am very new at this, so hopefully someone with more experience - or who plays a chemist on TV

- can provide some more clarity for you.