I opened my pool only a couple of weeks ago and have noticed that the pressure at the return jets and suction in the skimmer is much lower than normal. We had problems with our pool shed (floor rotted due to water) so had to get a new floor in. This involved moving the sand filter with the sand still in so don't know if this could have caused a problem (leak?). I've tried to eliminate each part of the system to see what could be wrong. On filter and recirculate the jets and suction are weak. On backwash and waste the suction is good. The pool is not losing water at any noticeable rate (no leaks from filter, no bubbles in pump) - I haven't had to add any water in two weeks. There is no algae problem and water chemistry is good. The setup is an 18x36 inground pool, sand filter, Hayward pump and solar heating.
I don't know what else I can test to see why the jets and suction are so weak. Any advice much appreciated.