My pool builder is pressure testing the plumbing with water. Pressured it up to 30 psi, went up to 31 psi later in the day, then dropped to 29 psi the next day. Stayed around 29/28 for 3 days. Pressure gauge is still on after 3 weeks and reading has dropped to 12 psi. We have had temps from 80 to 24 here in Tucson during this time. Is this pressure drop to be expected after this amount of time or do i have a small leak?