Barring testing your water quality, the best way to ensure it is adequate is by doing frequent, small water changes. This could mean 10% daily or more, depending on the size of your tank. Water changes aren't really an 'occasional' thing'. You need to do them regularly, not just when things look bad.
Those gills aren't 'cute'. They look ammonia-burnt, or at the very least they're scraggly. They're not normal, and you need to get to the root of why.
How big is your tank? How much water are you changing and how often? Nikki mentioned temperature. This is an important part of keeping axolotls. They're from glacial-fed lakes, and must be kept cool. They don't do well at temperatures over 20C for long periods of time.
You keep posting threads about how you think your axolotl is sick, but then you refuse to take any action toward making the tank better, or even providing us with any information about the tank. I'm not sure what you're expecting here.
