Right, some things just from what you've given us:
1. Might be an idea to get the temperature down a bit- a large fan straight onto the surface of the water works wonders.
2. Tank size- Having done small tanks with axies myself, it's a very difficult balancing act to do long-term. Each axie needs at least one hide (and one spare), you really need to make sure your tank is PERFECTLY cycled, and your water changes (2L/day works well) need to be frequent and thorough. Also, the better you can filter the tank (Without having the water flow getting too high- this will make your axie lose the rami/fluffy stuff and cause MAJOR freakouts on everyone's behalves). It's a good idea to start looking for a bigger tank (e-bayyyyy!!), and start thinking about shifting them to bigger accommodations

Be warned- tanks are addictive (I went 20L>200L, and I'm about to go to 400L min

)
Also, make sure you're listening to what your axies are telling you- if something's wrong, they'll put their gills forwards, and may even follow you to get your attention (As my original boys did when the 20L they were in to escape the summer heat crashed)
3. Levels- Don't worry- we don't want the levels off the top of your head, you need to do the tests to know, and because your tank's so small, it's a good idea to be doing them every day or two to monitor the chemicals that can be very dangerous to your axies. Don't use the strip tests- they don't work, get one of the tests with the test tubes- they're accurate enough to catch things before they go spiraling out of control
Welcome to axie-holics-anonymous!