I noticed that my pressure gage has not increased since I had the pool installed in June. It is at about 3 1/2 PSI on low speed and about 13 1/2 PSI on high. If I block the frow of water at the return on low speed it will rise to about10 PSI then drop back down while I am still blocking the flow. Is this normal? It's a Clearwater 2600 sand filter W/ what they claim as a 2 speed 2.5 HP 120v pump.