There is plaster on the inside of the pipe?
Some of the pipes have pebble-coat in them (stuck on...chips free pretty easy with a butter knife), and some of them have overhanging globs of pebble-coat that would prevent the nozzles going in (harder to deal with and the reason I think I will drain the spa to below the jets to sort this out).
I have (1) nozzle in enough I think it won't asplode and will try a test as soon as possible.
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Those are just for directing flow. They won't change the strength much.
I am more concerned with minimizing the gigantic bubble action to something more reasonable than altering the strength.
Although I am confident I would score metric tons of points with the wife if I could find pulsating jets to fit in the existing pipes.