Stains in fiberglass pool

[VinceL]

This is our third season for our fiberglass pool. The past 2 years, when we opened the pool, there were quite a few leaves in it. We got the leaves out, balanced the chemicals, and had clear water and a clean pool for the summer...no staining. This year, we opened the pool, got the leaves out and found that nearly 2/3 of the pool surface is stained...kind of a yellow/green/brown color. The staining is in all areas of the pool with patches of unstained areas. Brushing it does nothing.

Test results after opening:
TA 60
CH 160
CYA 25
pH 7.1
Salt 2200 (added 2 bags, now at 2900)

At first I thought it was algae. I tested and found .5 CC...hardly a high reading, but I had always had 0 in the past. So, I got the chlorine up to about 11 and kept it there for a few days. The stains remained, but the CC was down to 0. So, I guess it's not algae.

Over several days, I lowered the FC down to 1. Still had a CC of 0. I added 1.5 lbs of Stainfree a couple of hours ago. I have tried brushing and don't see any reduction in the stain.

My current readings are:
TA 80
CH 200
CYA 30 (keeping it low to get FC low for Stain Free)
pH 7.2

We have city water.

I know I am supposed to vacuum 24 hours after putting in the Stainfree. I'll give it 24 hours to fight the staining. If the Stainfree doesn't work, I don't know what to try next.

What could be the cause of the staining?

 

[JasonLion]

Try placing a vitamin c tablet on one of the stained areas and see if that does anything.

 

[rcy]

I've used Stain Free before - it's Citric Acid. If it's metal staining, you'll usually see it disappear right before your eyes when you add the product.

 

[VinceL]

I've used Stain Free before - it's Citric Acid. If it's metal staining, you'll usually see it disappear right before your eyes when you add the product.

While they don't list the ingredients, like you say, my understanding was that Stain Free is really just citric acid. I had figured (hoped) that I would see the stains just fade away right after adding it. But, after a couple of hours, I couldn't see any sign of the staining going away.

Once the rain stopped about an hour ago, I followed JasonLion's suggestion of putting a Vitamin C tablet right on a stained area. I put a few Vitamin C tablets on a stained area, and there was a slow clearing of the stain around the tablets. So, I guess it is metal. Don't know why we have it this year and not in prior years.

Now that it has been several hours since putting in the Stain Free, it seems that overall the stained areas have lightened a bit. Or, maybe that's just my eyes and my hopefulness playing tricks on me.

I guess it's time to buy some ascorbic acid...quite a bit cheaper than Stain Free.

 

[VinceL]

UPDATE

It's been a bit over 24 hours since I added the Stain Free. I would say 90% of the staining is GONE!. I guess it just took a long time for the Stain Free to break up the staining.

I ordered 5 lbs. of ascorbic acid yesterday. Hopefully, it will arrive on Friday or Saturday, and I can add some of it to eliminate the remaining stain.

I am still baffled as to why we have had this staining this year. Nothing about the pool or pool equipment has changed in the past 2 years.

 

[rcy]

That's good news. Don't forget to add metal sequestrant so the stains don't come back.