I have very low ph levels in my in ground pool. I opened it last week and since have added almost 50lbs. of ph increaser but the level still remains well below normal. Presently, I have an estimated ph of 6.8 or possibly lower ( doesn't show a reading below 6.8). Is this normal to add that much ph increaser or do I have another problem? Also, the plastic "spa step" area at the shallow end of the pool has turned yellow even though my water is crystal clear. Any ideas?