I am useing n2 and posed this same question about 3 weeks ago, I was not too concerned because I was changing the water, the water is now about 2 weeks old and I now have high ph and alk levels, I had never had high levels before, my dealer said that it was due to the temp outside vs the temp of the tub (I brought the temp down to 95 for the hot mounths) I just put in about 6oz of ph down and that seemed to put the ph at the proper level, so from what I understand it has something to do with the outside temp.