there are a few things that have same symptoms,
gravid.. when a female is gravid she puts on size due to the eggs inside her, this can happen whether a male is present or not, it has also been known for females to loose appetite and can take a few weeks to resolve itself, by which time her body will reabsorb the eggs.
osmotic bloating.. this occurs due to lack of salts and minerals in the water causing the water in the surrounding area to be absorbed into the body to balance out levels, this is why it is even more important to always re-add salts and minerals when using ro or distilled water.
organ issues.. liver failure which isn't very rare with axolotls and can cause a build up of fluid.
100% holtfreters is 3.5g/l sodium chloride (non iodised salt), 0.2g/l bicarbonate of soda, 0.1g/l calcium chloride, 0.05g/l potassium chloride, 0.2g/l magnesium sulphate (epsom salt) is added to holtfreters to provide additional essential mineral, 50% is half levels.
maracyn is an antibiotic which can be used with axolotls.
roobis tea has been known to be used with axolotls.