Water swishing in sand filter while vacuuming, why?

[antonaki1]

Recently i seem to be having trouble getting a full prime in the pump basket while vacuuming my inground pool, There is two small circular whirpools of air bubble near the top of the pump basket when i look through the glass. I can feel the water in the Jacuzzi sand filter swish around near the top and i think it is because of lack of full prime. I allways have full prime when in regular filtration. This only happens when vacuuming. Because of that i think i am sending alot of my post shock algae dust back into the pool through the return line. There are also bubbles coming out of a small pen size pipe in the bottom of the strainer basket at the pool where i attach the vacuum hose atop the basket. Is it normal to get some small bubbles coming up out of the strainer basket while in vaccuum mode. Hose has been replaced and the water is about a half inch above the recommended line, so plenty of water, pump seal is lubricated and airtight. Is it normal to have swishing of water in sand filter while vaccuuming?

[Backglass]

When you vacuum, your flow decreases quite a bit. If your pump is over-sized for your filter and lines (common...more money for the pool people) this can cause it to suck air through valves, lid gaskets and other places it normally wouldn't. The swishing you here in your filter is this air.

If the bubbles go away after vacuuming I wouldn't sweat it.

If you are seeing dirt come back through your return, then your pump may be channeling through the sand...another symptom of an oversized pump.