Best if you buy a thermometer asap. It's ok letting light into the room, but if the tank temperature is over 20C then you may have to use cooling methods to bring the tank temperature down. See:
http://www.caudata.org/cc/articles/cooling.shtml
A good method is to use a fan blowing across the surface of the tankwater (pedestal fans are good for this as you can change height and angle of the fan without worrying about it falling into the tank - I've seen members take photos of the small desk fans that they propped on the tank top aimed downwards to try and cool the tank), this brings the temperature down a couple of degrees.
Also, freezing bottles of dechlorinated water (3/4 full as ice expands); and then floating them in the tank. You have to rotate bottles, so as one melts and before its completely melted put another bottle in the tank, to maintain cooler tank temperature.
If you add styrofoam/polystyrene round the exterior of the tank (back and sides and front if need be), this will also help maintain cooling temperature longer (which can be handy if you work during the day).
Otherwise failure to cool the tank and maintain it below 20C can stress the axolotl and make it sick. When this happens the best place to put an axolotl is in the fridge.
If temperature is fine (you need to monitor it daily), the axie may just be enjoying the plants (hangout mode is common especially if there are plants in the tank).
One thing you have to be a bit vigilant about during the summer months other than temperature is water quality. 10=14 days can be too long to leave the tank for a waterchange as if there happens to be any ammonia or nitrites in the water the temperature can speed it up faster; especially with there being gravel in the tank. Gravel (especially if it has an undergravel filter) harbours waste. A lot of gunk builds up beneath the filter plate and beneath the gravel; despite being siphoned; hence the need to check the water parameters (ammonia, nitrite and nitrate) weekly and siphon more regularly (weekly) than 10-14 days.
pH levels do not need to be adjusted if they range between 6.4-8.0 (axies can live in those pH levels, so no need for adjusting those - pH up and down are only temporary fixes). Only thing is if pH is 8.0+ and there happens to be any ammonia in the tank then the ammonia is far more toxic.
How large is the tank (measurements)?
Other than that welcome to the forum and keep us posted!
On another note: Don't be tempted to buy things the petshop may try and sell you to fix the water parameters (this can be fixed by frequent partial waterchanges - 20=30% waterchange when needed; ie ammonia or nitrIte levels over 0) or give medicine to your axolotl (most fish medicines are toxic to an axolotl)