Hi mpikis,
The wound on your axie's foot is getting gangrenous. The tissues are dying hence the darkenened, malformed appearance. The tips of the toes which are reddish are active sites of inflammation. Complications can set in, including secondary infections by fungus and bacteria.
At the high temperature the axie is kept in, the axie is also stressed and immunocompromised. It can no longer fight off the infections as easily. What i am afraid of is that wounds like that can in severe cases lead to bacterial septicaemia, in which a bacterial infection release bacterial toxins into the bloodstream. This is fatal.
I suggest what you do now is to fridge your axie immediately. Fridging your axie will destress it, boost its immune system and render harmful pathogens (both bacterial and fungal) less viable.
- Set your fridge to about 5 degree celsius.
- Put your axie in a container large enough to allow it to stretch its limbs and tail comfortably.
- Fill with fresh dechlorinated water enough to submerge it but not allowing it to float.
- Cover with a lid. You can use a perforated lid or netting to prevent it jumping out.
- Use a tea towel to cover it to keep the environment dark.
- Perform 100% water changes daily with clean dechlorinated water.
- You can pre prepare bottles of water in the fridge.
- Continue to offer a variety of nutritious food daily. Try live wriggly food like blackworms, bloodworms, earthworms. You can also try the usual pellet, offer treats of shrimp and fish etc. Otherwise you can also blend everything in a food processor and then roll the resultant mash into a pea sized ball to try offer your axie. Remove uneaten food within 20 min.
I would try fridging your axolotl for 2 weeks and continually monitor for improvement. Please update on the progress every couple of days. Meanwhile, this would buy you some time to work on rectifying your main tank and gather the necessary items.
You definitely need to invest in a colourimetric solution type test kit that at the very least, tests for ammonia, nitrites, nitrates and pH. You should test your water at least once if not twice a week. You want to aim for 0 ammonia and nitrites and <60 nitrates. pH should ideally be neutral around 7. To keep the water parameters well within range, you would need to perform regular 20% water changes and siphon up detritus and uneaten food.
http://www.caudata.org/cc/articles/cyclingEDK.shtml
http://www.caudata.org/cc/articles/waterquality.shtml
Secondly, as well adviced by the others, you have to keep the water temperature down, ideally around 16-18 degree celsius without excessive fluctuations. The best way to do is to invest in a chiller unit. However there are other ways to keep the temperature down. If your tank is in direct heat or light source, move it to somewhere shaded and cool. Use mesh netting tank lid rather than a full glass lid to increase evaporative cooling. You can try mounting small fans on the tank to further improve evaporative cooling. Take a look at the equipment in your tank, are you using a submersible type filter? Such filters can generate excessive heat. You might like to consider a mini external canister type filter or mounted waterfall type filter.
http://www.caudata.org/cc/articles/cooling.shtml
http://www.caudata.org/cc/articles/filters.shtml
There is no necessity for 8 hours of aquarium lighting. Six hours of lighting per day will suffice. Try to coordinate your lighting period during the day time so that there is still a regularity in light hours. Reducing the hours of lighting will also prevent water from heating up.
You can keep your axie tank bare bottomed or use sand. Suitable types of sand include pool filter sand, freshwater aquarium sand or children play pit sand. Only an inch depth of sand is enough to prevent air pockets from forming.
Cheers