Black Stains on Liner

[TreeFiter]

I have a pool that I take care of that has extensive black staining on the liner. The staining is mostly in the deep end where leaves and debris accumulated while it was closed. The pool hadn't been opened for two years, and was opened again this year. There are a few small stains in the shallow end which are shaped like curled up millipedes. So it seems kind of obvious that the smaller stains are probably from metals leaching out of the millipedes and staining the liner. Is it reasonable to assume the large stains in the deep end are from metals leaching out of leaves and whatever else was sitting on that liner for two years?

How likely is it that I'm seeing Manganese staining? I'm assuming I can treat manganese about the same as I would Iron.

I added a sequestrant to the pool, and I'm hoping it will help. If it doesn't, what else should I try? Maybe Ascorbic Acid? Has anyone tried Ascorbic Acid (Vitamin C) treatments?

 

[JasonLion]

It is very likely that these are organic stains and will clear up after a couple of weeks at a slightly elevated FC level.

It is easy enough to try a vitamin C tablet on the stains, rest the tablet on a stained area and see if the stain clears up in that spot. If so they are indeed metal stains and it will be worth doing an ascorbic acid treatment.I doubt that vitamin C will have any effect, however it is simple to check and worth ruling out possibilities.

 

[TreeFiter]

What do you mean by Vitamin C tablets? The vitamin C treatments I've always seen are usually grannular. Do you think a vitamin C tablet like you would buy at a healthfood store would work in a pinch?

Also isn't there something about lowering chlorine levels before doing a Vitamin C treatment? I've never done one before, but I thought I remembered reading something about that.

 

[JasonLion]

If you want to do an ascorbic acid treatment to remove the entire stain, then yes you need to lower FC to zero and take other precautions. However, if all you need to know is if an ascorbic acid treatment is going to help then a simple grocery store/health food store Vitamin C tablet placed directly on the stain is all you need.

The tablet will only work in a very limited area, will use up a little chlorine, and isn't really an effective stain removal approach, but it will tell you if ascorbic acid is going to help. If an ascorbic acid treatment is going to work, you will see a dramatically cleaner spot right where the tablet was sitting after leaving it in place for a couple of minutes. It will generally not have any affect at all if an ascorbic acid treatment is not going to work. If the stains are light colored copper stains it can occasionally make things worse in that specific spot, but your stains are not light so that isn't an issue here.

 

[TreeFiter]

Awesome! I'll have to give it a try next time I'm there.