Dilemma after today's Vitamin C experiment

[Fuldo]

My pool in-ground Gunite and white pastered pool was brought back from the dead after I purchased it with my house almost 6 years ago. I've been using TFP procedures and guidelines the last couple of years and the pool seems to be well in control and very predictable. There has been a "tint" to the plaster since it was well cleaned and acid washed by a pool company directly after my purchase. The tint is slightly blotchy but in general is a slight tan color. In addition, there are probably eight spots about 2 inches or so across that stand-out on the bottom and they have a "rust" appearance. These abnormalities have been very consistent since I've owned the pool.

I recently learned from this site that Ascorbic acid can be used to remove rust spots and that trying vitamin C tablets on a stain is a good indicator that the stain is indeed iron. Today I bought some vitamin C tablets, put maybe 1/4 cup of them into a white sock and placed the sock over one of the "rusty" spots. I did this with the pump off. About 45 minutes later the spot turned from a rust color to an almost black color with about the same intensity. The most interesting thing is that the plaster near the sock and "downstream" was "bleached-out" and noticeably brighter.

What does this say about "rust spot"? What does this say about the discoloration of the plaster? It seems to indicate that the plaster discoloration is iron staining but that doesn't make a lot of sense because the water used to clean and fill the pool was local tap water that seems to have almost no iron content whatsoever. It sure would be nice to "brighten" the pool!

All thoughts and suggestions would be greatly appreciated.

 

[JoyfulNoise]

It’s likely copper stains. Copper will oxidize further on exposure to ascorbic acid to a black/brown copper oxide.

You need to treat the pool for copper stains. Jack’s Magic has a protocol and chemical regimen for it but, unless you dump the water after stain removal, your water will always have copper in it.

Do you know the history of chemical use in the pool? Did the previous owner use copper based algaecides?

 

[Fuldo]

Are you saying that the small rust colored spots are likely copper staining? If so, why would they be so localized? What about the overall plaster discoloration that was brightened by the ascorbic acid? Based on what happened aren't these likely two separate issues that likely have two separate solutions?

I don't know the long history of the pool. However, after I bought it about 6 years ago, it was completely drained, acid washed and refilled with tap water. It was mostly maintained by a pool service company until about two years ago when I took over. For a short while I struggled with a number of issues (as did they) and did resort to using copper algaecide more than once but never over did it. I think the overall discoloration has been there since the initial cleaning. About 18 months ago I drained 60% and refilled with tap water to resolve the excessive CYA problem caused by using tablets. Since then no algaecides have been used and there's been plenty of water exchange due to rain and drain so I suspect there's little or no copper left in the water.

The few dark spots I could live with, it sure would be nice to whiten/brighten the entire pool as the ascorbic acid did in the general area it was placed.

 

[gavin123]

Are you saying that the small rust colored spots are likely copper staining? If so, why would they be so localized? What about the overall plaster discoloration that was brightened by the ascorbic acid? Based on what happened aren't these likely two separate issues that likely have two separate solutions?

I don't know the long history of the pool. However, after I bought it about 6 years ago, it was completely drained, acid washed and refilled with tap water. It was mostly maintained by a pool service company until about two years ago when I took over. For a short while I struggled with a number of issues (as did they) and did resort to using copper algaecide more than once but never over did it. I think the overall discoloration has been there since the initial cleaning. About 18 months ago I drained 60% and refilled with tap water to resolve the excessive CYA problem caused by using tablets. Since then no algaecides have been used and there's been plenty of water exchange due to rain and drain so I suspect there's little or no copper left in the water.

The few dark spots I could live with, it sure would be nice to whiten/brighten the entire pool as the ascorbic acid did in the general area it was placed.

Just wondering if you ever did the Ascorbic Acid treatment? I tested with a few Vitamin C tablets and noticed the same thing. A black round stain where the tablet was sitting - and further away from the tablet the pool was noticeably brighter? I know I have iron in the water from a well - I wonder if I have copper too - or perhaps if you leave the tablet to fully dissolve it somehow turns black