I am in the process of slamming our pool. I have been filtering and backwashing since last Friday. Everything was going good until I went out to test this morning and my water was about 4" below skimmer level. I knew it was getting close to me need ing to add water and I planned to do that this evening, but it dropped about 6" over night. My question is, once the level gets below the skimmer, should it drop rapidly if the pump is going?