Tan-ish colored stains on fiberglass that are rough

[captjohn]

I use well water and have had these stains off and on for years. I use about 4lb of citric acid to remove them and the water sparkles and pool is beautiful when finished. Chlorine use is high for a few days after treatment and I aireate w/ jets, water fall and slide to bring ph up. I've tried several sequesterants, Regal Metal Out, Aquachem Metal and Scale, etc. and I don't see where they help. I use a TF100 and have to use the copper method to test ch. I wanted to have it tested for metal today but since it's stained now, the metals may not show on a test. I don't get any rain water and I use bleach.
Any ideas?
fc-6
cc-.5
tc-6.5
ph-7.6
ta-140
ch-110
cya-50
temp-88

My well water is:
ph-7.3
ta-220
ch-60

Even if I test + for metals which is probably a given, what's a treatment that may work?

 

[JasonLion]

The idea behind sequestrants is that they bind to the metals and prevent them from forming stains. Sequestrant breaks down slowly, so you need to constantly add more to replace the portion that has broken down recently. If you use the correct dosage of a good quality sequestrant and maintain it, you won't get any new stains.

 

[captjohn]

Any suggestions on brand? I've used the ones I listed as recommended and even on the heavy side without satisfactory results.

 

[JasonLion]

ProTeam's Metal Magic and Jack's Magic the Pink Stuff (regular), the Blue Stuff (fresh plaster), and the Purple Stuff (SWG) are some of the top sequestrants. You can also find many other brands with similar products, some of which are noticeably less expensive. Sequestrants based on HEDP, phosphonic acid, or phosphonic acid derivatives are the most effective.

 

[captjohn]

Thanks for the info.
SWG is the next project and may be soon!