Ascorbic acid tablet. Stain turned black

[alex-tx]

So I had a little mustard algae. Used the copper based algecide, shocked with chlorine. Life is good. I notice a little staining on the walls and the bottom of the pool. Scrubbed regularly, its still there.

Been doing (what I thought was) research on this site and in the pool school. Thought I likely have some staining from metals going on in my pool. Likely iron as we are on a rural water supply out here. Did the test with an ascorbic acid vitamin. Found a brownish stain near the steps on the pool. Rubbed the tablet onto it and the stain turned black. I wasn't ready for that. Fortunatly, I didn't think I knew what I was doing and dumped a couple pounds of ascorbic acid in there! I'm guessing some of the Copper is still in the water, but, I did not expect the reaction I got.

So, from the collective genius and experience here on this board, whats going on?

Thanks for everyone that keeps this board going, it has been a huge help for me for years as is evidenced by the fact that this is the first thing I have run across that I could not answer from the pool school and the forum and actually had to register and plead for help.

Approx 20,000 gal gunnite salt water pool, Intellichlor generator. All my other chemiclas look OK.

 

[JasonLion]

Copper stains come in several colors and depending on what color they start out as, ascorbic acid can sometimes change them from one color to another instead of removing them. Try putting some dry acid in a sock/stocking and holding that against a stained area for a minute or so.