Kinetico Water Softener

I have a twin tank Kinetico that is approximately 12 years old using potassium chloride. No pre-filter installed. About a month ago, while in the shower, I was getting a water surge and then reduction in water pressure. This happened several time, always when the shower was running. Three days ago the water to the entire house shut off. I bypassed the water softener and the water came back on. Obviously something is plugged. How to fix it???