Question about minimum tank size

[Aaron_likes_amphibians]

I see some people saying that a 20 long is too small for an axolotl and that the bare minimum is a 29 gal. I have been keeping mine in a 20 long for a year now and I have not had any major issues with water parameters. Is my tank too small or not?

 

[AMurry24537]

While tank parameters is always a concern, my tank sizes have predominantly depended on the size of my axolotls and how much they like to move around. I currently use 20 gallons for most of mine, but am thinking of upgrading them because several are pretty large. My 12" (almost 13") boy is in a 40 and I'm genuinely thinking he needs even bigger.

 

[JM29]

Since axolotls are mainly bottom dwellers, the soil surface is almost as important as the water volume.
Some 0,1 square meter by adult axolotl seems to be the strict minimum.