There is a few possibilities...
1- If the chipped carbon track does not go fully across, the wiper can be bent to track a healthy part of the carbon. Takes skilled hands, but done it successfully several times.
2- Visit a TV/whatever service center, they may have an used equivalent transplantable potentiometer.
3- Visit in person part stores, same reason.
4- Use your fan controller or a plain 600W+ light dimmer, it may well work, I do not see risk of damaging the chlorinator.