Quote Originally Posted by gogolion View Post
One thing I've never understood, which could be a cause of poor suction, is that air always seems to get air in my system when I vacuum. Air is always gurgling out of the returns. I have no idea where it comes from since no air gets in when I am filtering normally.
Sounds like a suction leak. If it is, it will probably get worse when you close the main drain. And, a suction leak will definitely impair vacuuming.

However, using a 1 1/4" hose, instead of a 1 1/2" will mess vacuuming up, as well. Also, stiff vacuum heads sit too high above the surface, and not create the high flow / high suction necessary for good vacuuming. The ProVac heads conform to the pool surface much better than any others I've used.