We have an in-ground spa, 6' octagonal x 4' deep (360 gals?). It only has (4) outlet jets, with (2) air makeup pipes in 1/2" pvc. Although we do get relatively good air mix & bubbles, one jet is so powerful, you can't sit near it. The other three are also a bit too strong, just not as bad as that one "super-jet". It has a 1.5 hp Hayward pump (90gpm@40' head), suction side about 30' long w/(6) 90 deg.elbows, all in 2" pvc. The discharge side is about 30' long w/(5) 90 deg. elbows, all in 1.5" pvc. I even tried running the spa with the jet outlets removed.
I'm wondering if that 1.5 hp pump is simply too powerful? Could the pump impeller be altered or replaced to reduce pump suction? Any suggestions as to perhaps adding a pvc loop accross the suction & discharge plumbing, with a valve to throttle some discharge water back to the suction side before being pushed out to the jets?