The difference between the two is that the 'regular' pH only tests the lower range pH (usually up to 7pH I believe) and the high pH test 7+. When you use the 'regular' pH, if it seems like the test says the pH is at its highest, double check with your high pH to see if it exceeds 7pH or not. When I first used the pH's it did that to me- my pH is about 7.2 but I wouldn't have known that if I didn't use th high pH. Usually betta's are pretty hardy and can tolerate in the 8.0 range- I believe the max is 8.2, but don't quote me on that; it's just the number I can recall coming up frequently when reading about it, but it's been a while since I've looked into it so it might not be 100% accurate. Sorry >.>;;