Asc. acid v. sodium bisulphate

[waterbear]

Actually, the light brown staining you see might be scale depost and not metal stains. .25 ppm is a very small amount of metal in the water...you said it was both copper AND iron. Copper usually produces brown stains while copper stains are either blue or grey black iron stains and blue copper stains are easy to remove. Black copper stains are difficult. Scale often produces a tan stain that is easily removed by acid since it dissolves the calcium carbonate, which is what a scale stain is. Since you said that the stains are easily removed by acid but not by a reducing agent I suspect they are scale. Dropping your pH to 7.0 for a period of time might remove them (and the reason the Metal Magic is removing them is because it does drop the pH of the water but you will have better results by either acid washing the pool or using a no drain acid wash kit such as the one by United Chemical.

I would be interested in a full set of test results. I suspect that your calcium levels are high, possibly your TA is high, and you have had periods of high pH which caused the staining in the first place.

[Carolina]

alk: 85
pH: 7.4
Calcium: 220

The older stains are caused by running my pool at a higher pH, and probably overchlorinating. This is something I've since corrected. However, recently (2 months ago) someone dropped a metal nut into the pool, which made half a dozen penny-like stains on the bottom.
Since then, light tan stains have been appearing all over the pool. An ascorbic acid treatment along with a sequesterant did nothing for them. I followed the protocol on this site exactly, hoping that it might work for me.

Would dropping the pH to 7.0 damage the heater? There is another site on the web that advocates dropping the pH to 6.0 for a day or so, but that seems to have the potential to cause too much damage.