Hard water treatment plant - Need to know the maintenance procedure for the filtration units

The community in which I live buys bore well water which is hard; the same is treated for hardness using three stage filtration units -

• Sand bed filter
• Activated carbon filter unit
• Resin filter unit.

We use about 1 lakh liters per day; inspite of regular back washing and re-generation using salt etc, the sand filter unit recently failed; the sand became solidified and had to be replaced.

Now we understand that since the unit is in operation for 2 years, both the activated carbon and resin have to be replenished/replaced.

• Is there a scientific way to know when these replenishment/replacement have to be done?
• How does one know if the back washing is done effectively?
• Is measuring the hardness pre and post treatment the only test to assess how effective the water treatment is?
• What purpose the meters (measuring pressure we understand) in each of the filter unit serve?

We shall greatly appreciate if some one educate us on these aspects. Thanks very much in advance!