Phosphate crystals for water treatment?
 

I recently moved to a home using well water. The water goes through a
string filter and then through a cannister containing phosphate
crystals.

The previous owner said when he changes the string filter every 3
months, he refills the cannister with phosphate crystals. I think he
said the phosphate was to reduce corrosion in the copper pipes.

The home is about 25 years old. I have not found anyone else near me
using phosphate. What are the pros and cons of this stuff?

PaulF