Soft water

[Leeatl]

I know this topic has been covered many times,and I have searched and read many threads ,but I have a different question...I think...lol We have a whole house softener that uses sodium,Our tap water is soft to begin with,3-4 on the scale,so it doesn't exchange a great deal of sodium to begin with . The system has a charcoal prefilter which removes chlorine and the like . I can bypass the softener for cold water but not the hot so I am not using that much softened water for water changes.My question is does anyone have any experience with using softened water and the rate at which the sodium builds up in the tank? I would think that if the water from the softener has X ppm of sodium consistently,then the tank can only reach the same ppm.Am I wrong in my thinking?If so let me have it...lol It would be a major pita to get the hot water unsoftened.Thanks.