How often do you do a waterchange?
Take a sample of tankwater into your petshop - ask them to test it for ammonia, nitrites and nitrates. Get them to write the figures down for each one. Don't buy anything to fix things if they say there is a problem with ammonia/nitrites or nitrates - you don't need it. Basically if ammonia or nitrIte levels (not nitrates) are over 0 you fix it by doing a 20=30% partial waterchange on the tank asap (same day you got the test done); thereafter you probably need to do it daily or every 2 days and make sure to remove any uneaten food/waste asap (invest in a turkey baster if you don't already have one).
Tank temperature to keep low is as crucial as water quality - especially if the temperature is sitting 24-25. If your axolotl is sick/ailing the temperature will increase its discomfort, lowering its immune system more which can lead to fungal infections or other illness.
If you can't keep your temperature down by using ice bottles/fan blowing across the surface, polystyrene method or moving tank to coolest part of house, particularly for your sick one, then ideally remove them both from the tank and place them in a container of dechlorinated water and into the fridge (as long as its 5C minimum or above). The fridging in particular, especially if you're working, will give you a few days grace so you don't have to worry to much (while at work) about trying to maintain a cool tank. This will also allow both axolotls to destress, slows their metabolism down, and will give your sick axie a chance to heal if its immune system is lowered/comprised due to heat etc.
For fridging you'll need two separate lidded containers (better to keep them separate).
Test the fridge temperature, if not known, by placing a thermometer in a cup of water and in the back of the fridge - check after 20mins.
If ok, fill both containers with dechlorinated water (tapwater with added water ager/conditioner/dechlorinater drops).
Remove your axies from the tank and place in the containers.
Cover with lid/s then wrap in a dishtowel and place in the fridge (the lid is to stop them jumping if they take fright; the dishtowel to stop the temperature fluctuations and light flashing from normal fridge usage).
Fill a couple of bottles with dechlorinated water and place in the fridge.
You need to do complete daily waterchanges on the containers at the same fridge temperature - this is what the spare bottles are for.
How long is your tank and how long is each axolotl?
