The pH chemical is not necessary. Your pH is up because of the shrimp. The pH from your tap is your true reading. Just do a 20% water change before your axolotls go in - use water changes to get the pH down. The pH adjuster should not be relied upon at all. If you drop it too low and the tap raises it, it will be harmful to your axolotls. Allow them to adjust to your normal pH - they can handle it.
Are you planning to cycle with the axolotls in? If so, then do a 50% change to get the pH down and forget about the shrimp (get whatever you can out), if you are getting the axolotls in a couple of days, there won't be enough of a start on the cycle to worry about.
It's never a good idea to play with chemicals in a new tank, it is vital to get accurate readings so you know exactly where you are in your cycle. Chemicals can cause you to get false readings, this could prove fatal to your axolotls.