Post return line repairs: Small spots on liner

[PoolDoc]

Hi Trae;

I can think of two other possible causes:

1. Copper oxide. Could be from a pool heater, or from a copper algaecide. Test by placing or holding a Vitamin C tablet against the spot for 5 minutes. If it lightens or disappears, it's copper.

2. Fungus from under the liner. Sometimes fungal colonies will develop under the liner. This usually happens when the ground is very wet and warm. There's no real test, except the color is IN the liner, rather than ON the liner. Unfortunately, there's no fix, either, since the source of the stain is fungal pigments bleeding through the liner from the dirt side.

If this is the problem, there are antifungal treatments you can do to the dirt / sand / vermiculite the next time you replace the liner.

By the way, if it's fungus, it usually will NOT be against the pool wall, but against the dirt / sand / etc.

[nalesean]

I will try the vit c. test tomorrow.

I have no pool heater, and haven't used any copper algaecide. It did have a sandpaper grit consistency and seemed to appear after the deck was cut into and concrete dust was scattered.

(The dots seem clustered around the two areas that had cut concrete.)

Is there any kind of reaction concrete dust can have that would bond it to vinyl?

Is it possible that the mini-rebar supports / saw blade cast off could have oxidized and made the pattern? If so the vitamin C test should help identify.

Lastly there is still some very tough grit that is stuck on the liner. Would getting a 100% nylon scrubbing pad and using that on the liner be safe for the vinyl? The pool brush just isn't helping at all. I was only able to scrape it off with fingernails.

[PoolDoc]

Bits of steel will absolutely stain a liner. Usually the stains will be orange, not black, but black is possible. If you suspect iron from that source, Iron Out offers a better test.

Buy a bottle of Iron Out (detergent section of Walmart, etc) and put 1/2 cup in a snack bag. Open the bag against a stained area, so the Iron Out gets wet, but is not washed away. Again, 5 minutes of contact should be sufficient to produce visible change.

Test grit with the snack baggie method, but use sodium bisulfate (dry acid or pH Minus). Wear plastic gloves.

[nalesean]

I'm still working on this.

I verified the vitamin C test didn't work.

I have purchased the Iron out, but haven't had time to apply it as instructed.

Will update after that.

Thanks!

[PoolDoc]

OK.

I just reread the thread -- it's possible for concrete to fall through the water and stick tightly to a liner. But, it won't usually be black. Just thought I should mention that.