My spa had a 1hp blower. It died and I wanted more air flow so I went with a 2hp. Wow did I get some air flow then, but it was a little too much. Then I had an idea how to reduce the air flow for about $5. I bought one small PVC pipe and one PVC coupler. I stuck them together and drilled a small hole. I kept widening the hole until I got the desired output. My final hole is about the size of a pencil. This does add a little bit more noise to the blower because you have the sound of the blower plus air coming out of the extra hole. I put duct tape on it but don't be alarmed, it's not going to fly apart. I had to beat those pipes together (I saw no reason to make it permanent).
Maybe this will help someone else down the road.

Maybe this will help someone else down the road.
