I have used dry ice a few times for Halloween as shown in this image:
https://www.troublefreepool.com/~richardfalk/pool/Cauldron.jpg
I had some leftover and put it into my pool -- not 60 pounds, of course. It is neat to see, but it does lower the pH quite a bit (it doesn't actually change the TA -- for the same technical reason that outgassing carbon dioxide only raises the pH with no change in TA).
Adding one pound of dry ice to 10,000 gallons would drop the pH from 7.5 to 7.0 if the TA is 100 and if all of the gas dissolved in water. 50 pounds in 10,000 gallons would drop the pH down to 5.4. If 10 pounds of their dry ice dissolved into 350 gallons in the spa, then the pH could have dropped to 4.6 which is quite acidic. In practice, about half of the gas escapes (bubbles away) with smaller quantities such as the pound or so I added to my pool (my pool's pH dropped from around 7.5 to 7.2).
Richard