Brownish-gray stains in vinyl IG pool

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David,

I cannot speak for vinyl liners only gunite/plaster.

Yes for my 9000 gal pool here in Honolulu I first got rid of all the chlorine. Then lowered, using Ben's calculator, the ph to 6 -6.2. Then added 1 quart of Algaeside 60 as a a preventative measure as we have lots of sun and I did not want an algae bloom

This was immediately followed by 1lb of ascorbic acid POWDER (not the crystals as these are non-acid and would not work). Then added 3 quarts of metal out to take the metal out of solution. Ran it through the filter for 48 hours non-stop adding 1/3 lb of DE to trap smaller particles. The 300 lb sand filter clogged-up pretty good after 24 hours so I back washed it for 1 minute only; leaving much of the remaining DE in the filter. At 48 hours it was pretty clogged so I backwashed it until it was clean.

The pool had never been treated for 10 years and as Hawaii's soil is mostly volcanic, "Red Dirt" as it is known, it contains a good amount of Ferric Oxide or if you like rust. The pool prior to this treament was dark brown to orange in other words terrible. After the treatment it looked nearly like new. Some light spots remain which I suppose are due to the stain being deeply imbedded in the plaster. No damage whatsover was done to the pool, pump, or filter. I did bypass the heater. I drained the entire pool to flush out the remaining iron in solution.

The ph of ascorbic acid I believe is 6.0 (MSDS sheet information) so I would guess no matter what ph you start with below 7.6 it would in any event take it down to 6.0 depending on the amount of ascorbic acid powder. So adding 6.0 to 6.0 would it really make any difference in few minutes time? I measured the acidity using a fish tank test kit about $10 which measures down to 6.0. Mine got as low as 6.2.

It might be that as I had so much ferric oxide in the pool this is why it did no damage, but I did it once again to see if I could get rid of the remaining stains. It helped a little but again no damage was done to the pool. I know that when the pool was built we had one of the best concrete persons in the state do the building. I got lucky that might be why the walls held up so well. The second time I did not drain it.

Finally being a little nuts and reading a white paper on agriculture put out by about seven state universities it suggested using Sulfuric acid to precipitate out iron versus ascorbic, in irrigation systems, which puts it into solution and therefore harder to remove unless you drain. So I followed their instructions and lowered the ph to 5.0. It quickly rose after 24 hours to 7. Did it help initially not a lot, but two days later it seems to have really worked wonders on those faint stains. I did use 1 quart of metal out, it only affected the alkalinity by lowering it from 90 to 60. No effect on calcium, CL or CYA, and contrary to popular believe the TDS was hardly affected. And certainly no damage to the pool at all, in fact to the contrary it looks better than ever.

I am no expert but this is my experience. Ignorance can be a blessing. Not having completely understood what I read on this web site may have been a blessing in disguise. Had I fully understood things may not have worked out so well. Many years ago when I was young I was selling my first little home in an enviroment of 15-17% mortgage rates. I assumed it was the realtors duty to show my home close to 24/7 not knowing this was not how it was done I harrased her and her boss constantly. The house sold at the asking price three days later. Some years later I had a realtor friend who explained to me how things worked. My next home took 1 1/2 years. I was carrying two mortgages, I wished I had remained ignorant.

I love this website and have learnt a tremendous amount especially from Mbar (Marie) and I enjoy the constant difference of opinions as it makes me think that much harder. But I do think you may indeed be correct with some concrete pools where the quality of the mix is in question. I tried to tell a good friend of mine that when pouring foundations for his home he should have a concrete engineer specify the mix and be on site to test it during the pour. He did neither, his foundations cracked, they had to be removed and re-poured, this cost him $60,000 plus.