Ascorbic acid, chlorine and TA (long)

Please bear with the long post. I think it illustrates some things that have not been discussed about ascorbic acid, at least not since the server meltdown. It also emphasizes that nearly all chemicals added to pool water can have unintended consequences.

Current values (read ahead to understand the trends)

FC 3 (and falling)
CC 0
TA 160 (and rising)
Ca 300
CYA 40
NaCl 3400


I have a 18 x 40 ~35k gallon gunite rectangular pool that is 2 years old. Sand filter, gas heater, SW chlorine generator, bleach to shock. At the end of last year, I noticed brown staining of the plaster, particularly at the junctions of the floor and walls. Brushing and high Cl levels did not remove it. While the pool store tested for metals, none were found, but I still strongly suspected iron as the culprit. I have never used copper or copper algaecides, and plumbing is PVC. Notice i do have a heater.

Upon opening the pool this year, i had a high TA (due to high fill water alkalinity and the pool store people accidentally almost completely draining my pool while winterizing--ugh, last time I let them to that service) and lowered it down to 130 using Ben's lowering ph to 6.8 and aeration method. Ph at the end of treatment was 7.2.

The stains remained from last year, so I decided to try ascorbic acid. I added an initial dose of 3 lbs., which removed most of the stains. I added an additional 2 lbs. after 2 hrs which pretty much made the stains imperceptible. Metal free was added after the addition of ascorbic acid. Ph was kept at 7.2.

So far so good. What surprised me was that my chlorine completely disappeared, and did not rise without adding bleach. As bleach was added, it too disappeared in 24 hrs, despite a working (as far as I can tell) SW chlorine generator. In addition, my alkalinity increased to 160.

Wondering what was going on, I googled "ascorbic acid" and "chlorine". It turns out there is a company called Integra chemical that produces ascorbic acid for use as a dechlorinator. It is called Vita-D-chlor (catchy, eh?) and according the the manufacturer it is 100% ascorbic acid, but has an MSDS for dechlorination of water. The MSDS also states that the decomposition products are CO2 and CO!

So, unless someone has a better theory, I am assuming the ascorbic acid is responsible for my chlorine demand and the subsequently produced carbonates for my increased alkalinity. Any comments or corrections? I have never used ascorbic acid before, and was wondering if anyone else had noticed these effects.

(BTW, www.pollardwater.com sells this product for 5 1/2 pounds for 45$, or 26 1/2 lbs for 180$ if you need a REALLY large amount. I do not know about shipping. If someone can find this cheaper elsewhere, please post.)

Disclaimer:I have NO affiliation with either company mentioned in this post

I can answer the chlorine question - chlorine is used up getting rid of the ascorbic acid. When I was first using the ascorbic acid I asked a guy from the chemistry strore what would happen if I still have chlorine in the pool and add the ascorbic acid - he said nothing - it would just waste some of the ascobic acid, because the chlorine will eat it up, that is why you should have your chlorine at 0 to start. I never had the alkalinity rise when I was doing the stain treatment - The ph goes way down, and is hard to raise after the treatment. I don't know what would have raised the alkalinity, what is your ph? Did you add any baking soda to raise your ph? I am not at all a chemist, but to lower your alkalinity your want to gas off the carbonates. The only thing I can think of is if you added baking soda to raise your ph, you would have also raised your alkalinity - you can use borax to raise the ph, it won't raise your alkalinity.

Thanks for the reply.

No bicarbonate...my alkalinity is naturally high and that is one additive I don't even have around.

No matter the cause, it looks like I am doing the "Lower the Alkalinity Dance" once again. Good thing I have a lot of muriatic acid. My fill water in eastern NC has an alkalinity of about 210.

Hopefully the stains won't come back!

Eric F

Oh, and my chlorine was 0 to start. I just was not expecting the chlorine demand after treatment, or the increase in alkalinity.

Thanks,
Eric F

You can see the best way to lower your alkalinity in this thread:

http://www.poolforum.com/pf2/showthread.php?t=191

You will start to hold chlorine when all the ascorbic acid is out of the water, it is always good to put in maintanence doses of metal free each month too.