Hi lilipad,
Firstly, i would recommend you isolate and quarantine your sick axolotl first. You don't want contagious diseases to spread.
You can do so by actually fridging your axolotl. Fridging your axolotl can help destress it, boost its immune system and render pathogens less viable/proliferative.
- Set your fridge to about 4-5 degree celsius.
- Put your axie in a container large enough to allow it to stretch its limbs and tail comfortably.
- Fill with fresh dechlorinated water enough to submerge it but not allowing it to float.
- Cover with a lid. You can use a perforated lid or netting to prevent it jumping out.
- Use a tea towel to cover it to keep the environment dark.
- Perform 100% water changes daily with clean dechlorinated water.
- You can pre prepare bottles of water in the fridge.
- Continue to offer a variety of nutritious food daily. Try live wriggly food like blackworms, bloodworms, earthworms. You can also try the usual pellet, offer treats of shrimp and fish etc. Otherwise you can also blend everything in a food processor and then roll the resultant mash into a pea sized ball to try offer your axie. Remove uneaten food within 20 min.
Meanwhile continue to ensure that your main tank has optimal conditions - check water parameters, regular 20% water changes, cool water temp, no excessive currents etc. Stress can cause your other axie to succumb to illness so you want to avoid that.
Bloat can be cause by renal dysfunction and scepticaemia. Take a look at these links to see if your axie resembles one with bloat. Try posting a photo here for comparison.
http://www.caudata.org/cc/articles/bloatEDK.shtml
http://www.caudata.org/cc/articles/illness3.shtml
Please also consider taking your axie to your vet for a diagnostic workup and appropriate treatment.
Cheers