The pumps we use are all AC (Conduction) motors...

You also could consider a Variac (Variable AC controller) to regulate its RPM. In the old days, Variacs used to be rather bulky actually still available today in the same fashion for bigger motors such as air conditioner fans or ceiling fans etc.
But nowadays they also exist in electronic mini versions as AC motor controllers via eBay and Amazon for a few bucks. If the description states it's an AC dimmer it should say it's suitable for fans, then you're good to go. Don't use single-phase light dimmers they will make the motor make a humming sound.

Best is to search for AC Motor Speed Controller, that's different from dimming.
Or switch to a prefilter setup and hook a DC pump to it and find a PWM motor controller, this also works a charm... I ran it for over 6 years without any issues at various speeds and in several experiments.
Always better to play with motor speed than run it full speed and reduce the flow through.