I can only tell you what I did and the results I received. We had our 26000 gallon pool installed this past March. Our water comes from and Iron rich south Texas well. I checked around for water delivery prices but no one could guarantee me that the water would be metal free. So here is what I did.

I purchased a whole house iron filter and put it ahead of my water softener.
I then estimated how many gallons of softened water could be created with each regeneration cycle. I used nothing but this pre-filtered softened water to fill the pool. It took many regeneration cycles over a period of 5 days to complete the fill. As a pre-caution I also treated the water with metal out and polyquat 60% algaecide. I should tell you that I'm also using a 26" sand filter with Zeolite filter medium. With pump on I let this mixture circulate for 3-4 days before turning on the SWCG. The water has been crystal clear since startup. I should also tell you that because I am running a salt water pool that I do not top it off with the softener as that changes the salt levels. I place a whole house iron filter on the end of the hose and fill from pre-softened well water. Hope that helps.