Hi, and welcome to the forum!
I can't think of any way that a water balancing issue would cause air in the pump basket--I think you need to be looking for a leak of some kind, albeit very small. A common culprit is the seal around the pump strainer basket--are you sure that it's tightened down enough? All the knobs on the filter tight? Any sign of water leaking out the backwash pipe when the pump is on, or water standing in the multiport? It only takes a very, very small leak to cause an air bubble. Are you sure that the water level in the pool is sufficient?
You don't have to shock a pool once a week, whether you use bleach or not--you only really need to shock it if your combined chlorine is over 1 ppm, or if you're losing any chlorine when testing at night and again in the morning before the sun hits the pool. When you do need to shock it, though, the level to which you need to raise your chlorine is dependent on your CYA level. See the "best guess chart" link in my sig for "shock" chlorine levels. In a pool your size, each 1/2 gallon of 6% bleach will raise your FC by 1 ppm, so you can use that as a guide when figuring how much you'll need. If you have any other questions, ask away!
Janet
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