Pool filter sand is nice because it looks more natural, doesn't cloud up like play sand, and doesn't get sucked up as easily with a siphon. Pool filter sand won't affect your pH. The only thing that will affect your pH is substrates which are calcium-based. You'll still have to wash it, regardless.
Why are you putting 60 kg of sand into the tank? That's outrageous! Even in my 4 foot tank, I put at most 3 kg in there.
You'll have to remove your axolotls, as no matter how well you wash your sand, it will make the tank cloudy. Take them out before removing the gravel, and put them in a large bucket with tank water. Take out the gravel, add the sand. If you have a filter, turn it off until the large particles of sand have settled.
For future reference, please use proper punctuation, as not everyone on this forum is a native English speaker, and it is hard to understand your posts without appropriate punctuation.