New pool owner - need help with ascorbic acid

[wal81]

I'm a brand new pool owner - I've read TFP pool school and this is my first post here.

We just closed on our new house with a pool. The previous owner has taken great care of the pool and equipment, and generally followed TFP methods. Three weeks ago, he did a treatment with ascorbic acid to remove metal staining. He added way too much, 6 lbs instead of the recommended 1 or 2 lbs (this is a 20,000 gallon pool with SWG). Two weeks after the treatment, he tested the chlorine level and found 0 FC. He shocked with liquid bleach and raised FC to 20. At the time the ownership of the house changed hands to me. Today, my first visit to the pool, I checked FC and it was back to 0. To buy myself a little time to figure this out, I added some liquid bleach to raise FC and I also turned the SWG up to 50% (it was on 10%).

Can anyone help me understand what is going on here, and what I need to do next? Is it harmful to have that much ascorbic acid in the pool, or does it eventually go away?

(pH is 7.2; CYA 50; do not have TA measurement; water has some settled pollen but otherwise looks pretty clear)

 

[JasonLion]

Welcome to TFP!

Large quantities of ascorbic acid (AA) are harmless, aside from using up a great deal of chlorine.

For AA, you just keep adding chlorine until eventually the AA is all used up. Chlorine and AA destroy each other quite efficiently, so as soon as you can hold an FC level the AA is gone. You don't need to rush to do this all at once instantly. The SWG will be adding enough chlorine to the pool to keep things from turning green, despite that chlorine going away almost instantly. However, don't wait too long as the balance isn't completely stable, i.e. you do get algae eventually.

One thing to do soon is to get a full set of water test results.

The final thing to keep in mind is that AA removes stains from the surface and puts the metals in the water. You need sequestrant in the water to prevent the stains from forming again. Sequestrant breaks down slowly, so more needs to be added regularly. Related to this, higher FC levels also encourage staining, so it takes slightly higher sequestrant levels to prevent staining at higher FC levels. Because of this you don't want FC to go up too high.

 

[wal81]

Thanks! So, I need to add bleach until the AA is used up, and then I can rely on the SWG like normal? How long does the chlorine last in the water before the AA uses it up? (i.e. how long before I can tell if I need to add more bleach...I don't live at the house yet, so weekly monitoring is more realistic than daily).

Thanks for the tip about the sequestrant - how often is it added? If higher FC encourages staining, what is considered high FC? I see the TFP recommendations are 4-6 ppm for SWG pools.

I will plan to get a full water test this week. Thanks again, great resource here!