I remodeled the back yard including cement around the pool a few years ago. I had the brilliant idea to replace the filter, pump and skimmer line at that time. It has never run well since then. The pool is very deep - 12ft in the deep end as it was built in 1970. 20x40, plaster. FNS 48 DE -use Zeno Fiber, Sta-Rite Superior 1.5HP. Always have bubbles in skimmer line, but no bubbles when the skimmer valve is closed. I have to clean the grids weekly or more often and the water pressure seems weak. Help???