Hi, we just had our liner replaced in our inground pool. New water...salt water system added salt. We had the water tested last week low Alkalinity and it needed calcium hardness. This past week the reading asked for more of the same chemicals. The pool store said turn on the heater bc its been so cool out. Nights 57. And retest in a few days. Any ideas what this is? I have a Hayward filter system 3025.