I had the same problem.
I used the pu,p valve. You have to play with its setting to get bubbles and have a reduced flow.
You have to have the water return exit ABOVE the water level. By having it below causes back pressure on the system and water has no where to go but up.
I dont even have the flex tubing on mine, just the 90 degree into the bubble trap.
The valve is a weird one (red) all the way in either direction is the same, fully open. If you pull off the return 90 you can see the gate in the valve. spin the knob back and forth, this will give you an idea of where the gate actually blocks the return line, there by increasing the water level in the skimmer.
Funny sounds like I know what I am talking about. Considering I was asking the same questions last week.
