First off don't panic!!
You will need to check your axoltl tank water for ammonia, nitrate and nitrites. If you haven't got the test kits ( I wouldn't use the 5 in 1 strips ) get the pet shop to test a sample ..write the ammounts down and then let us know.
If I remember correctly you have 2 filters running, is that still the case? also do you remove unwanted food and spot clean..they can be messy little beasties. You'll need to do weekly 20 % water changes with dechlorinated water.
Finally ( for now) what size tank are they in and what is the tank temperature if its over 20 degrees it'll start to stress them.