I have been fighting a lack of bubble from my in-ground spa for a couple of months now. I have read more than two dozen post of people that have the same symptoms as me:
-Jets stopped blowing bubbles out of the blue
-When you lower the spa level the jets would work
-If you blew air into the air intake the jets would work
-Jets have plenty of water flow, just no bubbles
Many people indicated they had repair personnel come out, none reported their problems were fixed. The most common suggestion was to add a blower to the system.
Well I finally caught a break in my diagnosis. There was an odd piece of PVC sticking out of one of the nozzles the other day. Pulled it out and after doing a little digging found that it was a Venturi Tee Nozzle. It appears that due to age and heat it deformed the tabs that hold it in place. I ordered new ones (less than $2 each) and replaced the missing one. The nozzle sprang to life shooting perfect bubbles. Replaced the other three and the spa is 100% again
Even though I still had three in place the deformation allowed water to flow around the Venturi Tee Nozzle killing the venturi effect. This made it where it didnot have enough suction to pull in the air. Hope this helps someone else. Picture shows deformed tabs (center) and out of round intake (left).