Hi, that's a very pretty Leucistic you've got there! Hi Atzi!
I'm glad that you've decided to use sand rather than gravel or stones....axies can accidentaly swallow stones/gravel which can lead to fatalities....
Make sure the sand that you get is suitable for freshwater aquariums (probably silica-based) rather than the sand pet-shops sell as 'reptile sand' or the like.
When you get the sand it has to be WELL rinsed, putting the sand in a bucket and sticking a hose-pipe into the middle of it, aggitating/stirring it until the water runs clear, then draining it and soaking it in treated water . Remove any pieces of gravel that might be in the sand.
Axolotls aren't really known for 'digging' into sand (or any other substrate) but I'm sure they'll appreciate the sand, and it'll be easier to clean than rocks, for example.
Hope this helps :happy: