As with keeping fish, the water in an axolotl tank needs to be clean. We use tap water in our tanks, but we make sure to dechlorinate it first by using Stress Coat or Prime brand dechlorinators. These are available at any store that sells aquarium products (PetSmart, Petco, Walmart, etc.). When you first set up a fish tank, everything is brand new, and there hasn't been sufficient time for beneficial bacteria to colonize it. These helpful bacteria turn waste material in your tank into less toxic substances. However, they need time to multiply and grow. This is what is called "cycling" your tank- these bacteria facilitate the Nitrogen cycle. (We'll add more on this section soon.) Basically, it's best to have your tank up and running, with water and filtration, for a few weeks prior to getting your axolotl. In our experience, they are quite a bit more tolerant of the ups and downs of water quality during cycling than fish, but it's best to have the water ideal before introducing them to their new home.
Water Quality & Regular Maintenance
Once your tank is up and running for a month or so, you will notice that your water starts to get a bit discolored. This, of course, is due to the waste in your tank put out by the lotls. We recommend changing part (but not all) your water on a regular basis. If you have a 20 gallon tank with one adult axolotl, you should probably change about 50% - 80% of the water in the tank every couple weeks or so. Keep in mind- the more axolotls you have in your tank, and the more you feed them, the more frequently you will need to change the water.
Water changes are pretty easy, really. Changing a small tank shouldn't take more than about 20 minutes. To remove the old water, we use a siphon hose with a hand pump that you can get at a fish store, or PetSmart, Petco, etc. Once the water is removed, we use a large water jug to transfer water from the faucet to the tank. Make sure the water coming from your tap is fairly cool, and that you have added dechlorinator to the jug before adding the water. (The chlorine in tap water is very bad for 'lotls and will make them sick immediately.) Some people opt for a hose to refill their tanks, and thus add the dechlorinator directly into the tank during refill.