Hi,
pH in Xochimilco lake vary from 5,7 to 10,4, with a median between 8,1 to 8,6.
(read : Perez-Belmont et al., 2019 : Water Quality Monitoring inthe Xochimilco peri-urban wetland : experiences engaging in citizen science - Freshwater Science 2019, 38 (2), published online)
So there isn't a real emergency.
How is your axolotl health now ?