Honey,

If the softener replaces the calcium with salt would it be possible for the
water heater then fill up with salt? I have been replacing my water heater
every 7 years and it is filled up something that resembles salt. I thought
I was safe because the heater is after the softener. Any ideas on what to
do to prevent this in the future?

NaCl is quite soluble in water whereas CaCl2 is not. It is really
unlikely that your water softener is filling up with NaCl.

Dave M.