I have kept axoltls for many years, just got 18 at the moment. Overcrowding causes them to bite at each other,dim lighting seems to reduce this. Live bloodworm is my food of choice for young animals that still require food that is moving but have got past the brine shrimp stage. I have had good results feeding top end (expensive) fish foods designed for predatory fish. Some of these are well balanced with vits and minerals and, in the UK at least, give detailed breakdowns of the nutritional values. I also use as wide a variety of other foods as I can, cut up raw freshwater king prawns give good growth rates but work out expensive!
This year I had more young axolotls than I could easily keep in doors so I put a few into a large plastic tub in my garden that I use for growing pondweed and daphnia, there are lots of things swimming around in there and they have done very well, they are not quite as big as those I kept inside, but I selected the bigger ones anyway, but they are much more interestingly and heavily marked, including some that seemed to be pure white when I first put them in.