How much KH (alkaline) do axolotl need

How much KH (alkaline) do axolotl need? That is my question. Cause I house lots of axolotl and for some unknown reason I could never seem to natually establish any KH level no matter how many years it has been. Still 0 or close to 0. So far I have been adding alkaline buffer for aquarium and my axie seems pretty happy with it. Of course my tap water alway 0 KH but even when water haven't been change it's still 0 KH I have to add buffer to get to 20 ( I don't want to add too much chemical in my tank just very as little as possible)

My tank before water change ( always like this)
Nitrate 20 - 40
Nitrite 0 -0.5
Chlorine 0
Gh 75-150
KH 0
Ph 6.8 -7.0

After water change 25% (or 50% if I would be gone a lot longer)
Nitrate 0-20
Nitrite 0
Chlorine 0
Gh 75
KH 0
Ph 6.8

So it sounds like you have soft water, you could benefit from Holtfreter's solution, it supplements soft water for the health of Axolotls, because they need hard water. I can only find one place to buy it, the research dept that keeps the Axolotl colonies. You have to print an order form and mail it with a check, here's their website to get the order form. Ambystoma Genetic Stock Center

Yes as you can see at 75 GH is considering soft ( not very soft but still soft) but I can easily kick it up to 150 with just little of aquarium salt . And yes you are very right!! I could use holtrefeter's solution since I do made my own, and It's away the best. I'm just little low on supplies right now so aqaurium salt would do. Still it doesn't seem to kick up any alkaline Unlike the alkaline buffer. My axie doesn't seems to be bother by it, but still I'm very concern about using it for the long haul. I'm not an expert chemist and the basic ingredient of akaline buffer still got me scratching my head debating if it's safe or if it's not. Since all I know so far is that Alkaline buffer solutions made from a weak base and one of its salts, it contains hydroxide ion. I don't know if it harmful or harmless to axolotl .