Cartridge filter

Air bubbles going back to the pool is an indication of a suction side air leak. Basically air getting "sucked-in" to the system somewhere between the poolside skimmer to the pump. The funnel thing, are you referring to one of the return jets? Something else? Maybe post a pic of it?
 
he funnel forms right in front of the out where the water is going into the pool.
Those are your return jets. Air bubbles aren't bad as in an emergency situation, but a sign that something is not quite right and you should explore it. Yours is a non-salt pool, so air bubbles would mean air is getting in on the suction side. Start at the pump clear lid and look under at the O-ring to ensure it is clean, serviceable, and has a generous amount of pool lube applied. After that, check anything else at the equipment pad for potential places where air could get pulled inward. Also be sure the water level is high enough in the pool so that the skimmer is nice and full and not gulping air.
 
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