If it’s a kalk stirrer that uses a slow spinning stir bar to mix the kalk solution like the K1 or K2 from Avast Marine, then you run it 24/7. If it’s a kalk reactor that uses a power head to mix the kalk solution like the one from GEO, Precision Marine or MRC, then that goes on a timer. The kalk slurry would destroy the impellers of the small power heads used on kalk reactors if run 24/7.