Well Water: Why you DON'T shock BEFORE using Sequestering Agent

[crackerjack]

I have staining problem from well water also when I have to fill from evaporation. The fiberglass steps stain slightly, but the vinyl liner does not show stain.
The Metal Free and Stain Free solution is getting to be expensive.
Did not seem to have that problem last year and the only thing I am doing different is instead of filling straight from well, I am feeding off of water softner and neutalizer (Rain Soft system) from house.
I have not done an iron test but I do know citric acid is the only thing that removes the stain from the steps.

Anyone think the Rain Soft system is the problem?

(Forgot to add that I do feed the water thru the skimmer)

Thanks
cj