Just curious if there is a set amount of time I should change out my RODI filters and resin? I live on a well and have been using the original for over a year now….. the resin hasn’t changed colors at all…. Testing from the tap I get 100 tds…. Have a meter on my RODI going into the di I get 1tds and always 0 out….. and testing the water with my tester is always 0 after…. Just curious if there is a length of time these filters expire in?