Happy Fathers to all you Dads and to Moms that take Dads place!

Well I put some vit C tablets in a sock and tried it on the house vinyl siding, it removed 90% of the stain.I then wiped ( just a light rub) the pool step it removed the stain 100%anf the steo was pure white. Brushing and rubbing with a rag did nothing to the stain. I will follow all of your suggestions and keep a better eye on the water chemistry.
One question when I used my new K -2006 the FC=.8 CC=.2.
When I checked it with my old HTH delux test kit the TC= 8-10. Using my old kit I kept the level between at 5-8. This looks like it was misleading me to believe my level was good.

Still think it is iron and not copper!!!