Hi,Last summer I bought a 12x12 Intex garden pool with a water filter pump. I somehow never had much confidence that the pump was doing very much and in fact, after a few weeks, the tubes turned green! I cleaned everything up and now I've set it up again for this summer. This time round I can see water flowing in the pipes... great. Except... the water flows nice and fast when the air valve is open (no water seeping out which I thought was odd) but when I close the air vent the water slows right down. Is the air vent supposed to be open or closed? My thinking is that faster flowing water = more efficient filtering? Thanks.