I've had to replace two expansion tanks in four years on my secondary loop of my Geo system. This loop is water only for a radiant floor system. I am using soft hot water for make-up through a B&G pressure reducer valve. The pinhole leak rusty water indicating internal corrosion. Should I look for a stainless tank or some kind of corrosion inhibitor in the water loop? Or is this indicative of some other problem? Thanks!