I have a fiberglass pool surface & Pool Pilot chlorine generator (approx. 13k gallons). About a month ago I noticed a few spots of rust on the pool steps and at the bottom of the spa. The rust appears in small circles and is a dark orange. I've had success removing the spots with a vitamin C tablet. I did some extensive pool maintenance this past weekend and noticed the bottom of the pump basket was rusted. I also cleaned the Pool Pilot filter screen and noticed some rust on that too. Concerned, I went to the local pool supply store and had my water tested. Phosphates were a little high but nothing too concerning according to them (I've since lowered them) but they found no iron nor copper in the water. So I'm at a loss as to the cause. My pool isn't particularly dirty and any leaves or debris are removed weekly if not sooner. I suppose it's possible the rust could be organic in nature but I'm not sure what product to use and whether that product will remove the rust off of the pump basket and Pool Pilot filter screen.
Thanks for any advice!