Every 6 weeks you should remove the pump cover and pull the impeller assembly out of the pump.
Soak the impeller in a solution of water and vinegar overnight.
Take a q-tip with vinegar to clean the cavity of the pump then rinse with water.
You should have a back-up impeller on hand so there is no real down time to your water feature.
It is essential to properly maintain your pump in order for it to function properly.