Axolotls are so neat. I used to have them when I was a kid. Of course, back then, we just called them "water dogs".

I agree with everything Fox Gal said.

Actually, the larger the tank the easier the chemical maintenance and clean-up is, IMO. My 55 gallon is way less work than my 30 gallon was, after the initial setup.

The do make completely submersible heaters, that can lay sideways on the gravel. I have two in my tank. I got mine at Walmart. I would put a guard around it though, so he doesn't burn himself.

Just curious about keeping the tank only half full. I remember we never did this with ours, we kept it almost completly full. They swim and dive like crazy if they have the room.

I think you should run the pump all the time. And I think he will consider a frog to be dinner, when he gets a bit bigger.