HELP! my tap water is unusable for water changes

[pickel!]

In fact, not really.
Nitrates are not very toxic by themselves.
Nevertheless, if you let them accumulate, you'll end with side effetcs like algae.

Nitrates is generally evidence of something wrong, like decaying organic matter in excess.
Here you know the cause is total ammonia brought by tap water plus ammonia excreted by your axie.
You also know ammonia is well converted to nitrates.

One way to control ammonia and nitrates together is adding real aquatic fats-growing plants.
Chose plants like Egeria densa, Ceratophyllum.
If you have no light on your tank, Java moss and Java fern will help but put a lot of them.

I've heard live plants are hard to keep alive since axolotls require such cool water. I'll definitely be looking into some hardy plants for the tank, though.

I was able to get some freshwater for a water change today to be sure we're not putting more ammonia back in the tank, I'll make sure to test the water first.

 

[JM29]

The plants I gave the names thrive well in axolotls tanks.
I have them in all my aquatic caudates tanks which are in my garage (temps varying between 4°C to 21°C on a long term)