Go to just above whatever the lowest reading on your pH test is.

You have to remember, that if 7.0 is the lowest reading on your kit, a reading of 7.0 does NOT mean that your pH is 7.0. It means that it is 7.0 . . . OR BELOW! It could be 6.8, which wouldn't hurt anything in your case. But it could mean 5.8, which would damage your liner fairly quickly!