Hi have a 20x40 ig that I need advice on. Upon initial pump start suction and return flow good. After hour sometimes less return flow reduces dramatically. Just opened pool so figure it's filter backwashing. Anyways if I do backwash and turn back on pressure/flow returns to normal, then again reduces dramatically after time. I know it may mean de grids need acid wash but I noticed today the flow coming into the pump(thru the pumps skimmer basket lid) was reduced dramatically. Isn't this before the filter and clogged de grids shouldn't affect this?? I do have bubbles at return when I first turn on pump then gradually stops.

Also I don't see any pressure change on de filter gauge during any of this. The gauge reads zero when off then goes to 10 during operation
Please advise where to begin