I could test the pH of my tank, but I don’t have the water from the bag anymore.What was the difference in the pH between the water in the bag and the water in the tank? You said you floated them for a half hour and released them with no acclamation to your tank water. I'll bet if you check the two there was a significant difference, if you get the numbers you'll get your answer.
Edit: All four Bala Sharks have died.