Calcium, lime buildup happens on the hot water heater elements. It will slowly kill your hot water heater. The best thing you can do is...
approx. every 6 months, turn off your water heater, let the water cool down. Maybe turn it off in the morning and flush late afternoon.
After its cooled down some, hook up a hose to the tank, open the valve and let the calcium buildup flush out the bottom. Close valve above tank to shut off pressure. Close valve to house hot water side. Let the hot water tank totally drain empty. Open water pressure valve, and let water flow thru tank again and out hose. Take a look where you have the hose discharging, you will see tons of calcium chips, pieces. After you are satisfied with flushing, close valve at bottom of tank. disconnect hose, open valve to hot water in house, make sure pressure side valve is all the way open. Now, run the hot water faucet for a long time to make sure all air is out. After water flow is all back and no air pockets, turn your water heater back on.
Cost? I see in some earlier post they said is cost a lot. I must be missing something. A whole house filter unit from lowe's is around $31 Change the filter... depends on what you see.. the clear plastic housing let's you see how dirty it is. Maybe change it every 6 months. It will really depend on how much sediment you have traveling in your system.