Kylez = did you cycle your tank, see:
http://www.caudata.org/cc/articles/cyclingEDK.shtml
If you didn't then the most important things to test are ammonia, nitrite and nitrate over the next few weeks. You can buy these from the petshop in a master freshwater test kit or individually. Most tend to use the API, Aquarium pharmaceuticals brand, the test tube variety, as it's more reliable than the all in ones or dip strip brands. Don't buy an ammonia binder or ammolock type chemicals as these will not help your tank cycle, it will just cause problems in the long run.
If you don't have a test kit for these then take a sample of tankwater to the petshop regularly, every few days, till you can afford the kits or at least ammonia one first, and ask them to test the tank water for the ones I mentioned. Then ask them to give you the figures, if they say its fine or toxic or something other than the figures, don't accept it, make sure they write the figures down and then most importantly DON'T BUY anything from the petshop to fix it (especially if they suggest you do so!)
Basically, your tank will start cycling since you added your axolotl, if you haven't already cycled it, and the ammonia/nitrite and nitrate are more important than pH to test while it does cycle. (Cycling can take between 3-10.5 weeks to cycle) If the test results for ammonia and nitrite rise above 0, you need to do a partial waterchange (only 20-30% no more). If you're unable to get the water tested within the next few days, then make sure you do 20% waterchanges every 2 days and clean up any uneaten food or waste spotted (buy a turkey baster if you don't have one, they're great for cleaning)
Be very wary about what the petshop advises regarding axolotls. If in doubt check here first, this forum is full of many experts, and especially quite a few australians that have found this forum, through inexperienced petshop people giving poor advice concerning their axolotls care and needs.
Also, the best food to feed axolotls is earthworms. If you have problems finding any then you can use, even now at that size (I'm assuming it's below 10cm) = mosquito larvae (found outside in water containers) or frozen bloodworm cube. Up until 10-12cm you can feed him/her twice a day, up to 15cm once a day, up to 20cm once every 2 days, over 20cm once every 3-4 days. This can vary depending on season/temperature. Some axies will eat more when it's warmer and less when its colder or as they mature.
If you've been advised to feed mealworms, you need to chop the heads off as they can bite the axolotl as it's being swallowed. Mealworms should only be fed as a staple.
What is the tank temperature? If you don't have a thermometer, make sure you get one, this will especially be important with your summer coming up (ideal temperature to keep them at is 18-20C during summer. Anything over 22-24C and you'll need to cool the tankwater so your axolotl doesn't get sick/stressed).