Polyquat-60 used with Ascorbic Acid Treatment

[gtm]

I’m just starting to let my chlorine drop in order to begin the ascorbic acid treatment and I have a few questions that I hope someone might be able to help with. All involve the application of the Polyquat-60 I bought to use while the chlorine is low, as suggested in the instructions for the ascorbic acid treatment written by mbar/Marie. I haven’t used an algaecide before.

First, though, here are my current numbers in case these are needed.

FC: 7.0
CC: 0.0
pH: 7.5
TA: 80
CH: 425
Borates: 50
CYA: 60
Temp: 67

First, when should I add the Polyquat-60? Now, or wait until the FC reaches minimum for my CYA, or wait until it hits zero just before I start the ascorbic acid treatment?

Second, what dosage? Instructions on the bottle say 11-16 oz. per 10K gal. for pools with just visible algae, or 6-11 oz. per 10K gal. for freshly cleaned pools. My water is very clear and I don’t have any excess chlorine use, so I’m pretty sure there’s no problem with algae at present. But would going a little heavy with the Polyquat-60 while the chlorine is zero make sense, or just interfere somehow?

Third, should I repeat the application while waiting for the chlorine to come back up? If so, how much and how often would you recommend?

Thanks in advance for any advice you can offer … Gary

 

[chem geek]

Gary,

I just recently did this treatment in my pool and I used the larger initial dose recommendation for PolyQuat. Also, if you use it while your chlorine is higher, the large dose will help to lower the FC faster since chlorine slowly breaks down PolyQuat and higher FC and higher PolyQuat doses make this go faster. The PolyQuat is still effective as an algaecide even when it is broken up into smaller pieces (though its ability to act as a clarifier is reduced). The PolyQuat usually lasts about one week between chlorine degradation and getting filtered out, but that's at normal summer temperatures. So you can add it now if you want to -- it may help lower the FC faster.

Note that the ascorbic acid is a reducing agent so will lower any FC in the pool. In a 15,000 gallon pool, 5 ounces weight of ascorbic acid will get rid of 1 ppm FC (and vice versa). So figure that into the amount of ascorbic acid you add since Marie's dosing of 1/2 to 1 pound per 10,000 gallons assumes no chlorine in the water. Also note that 5 ounces weight of ascorbic acid is equivalent in its acidic effect as 2.7 fluid ounces of Muriatic Acid (31.45% Hydrochloric Acid).

Unfortunately, the treatment didn't work well for me, but my iron stains were very old -- almost 5 years. They do seem to have faded a very little so I may try this again with a more direct treatment right on the stains.

Richard

 

[gtm]

Thanks Richard!

I understand the Polyquat-60 thing much better now. I read here somewhere about it using up FC, and mistakenly thought that meant it was "used up" and more would be needed. Your explanation makes it much more clear now. I think I'm good to go as far as the Polyquat thing goes.

Thanks also for the ascorbic acid, muriatic acid equivalency. I was wondering about that and searched a bit for it without success, and in fact the numbers you give make me wonder. I hope you don't mind a follow-up question.

In the instructions for the ascorbic acid treatment, it's mentioned in several places to be sure not to let the pH rise above 7.2 for a "week or two" after adding the ascorbic acid and sequestering agent. But if I add 1.5 lbs. of ascorbic acid, call it 25 oz., then I get the equivalent of 5 x 2.7 = 13.5 oz. muriatic acid, which (according to the Pool Calculator) will drop my pH by 0.2, or to 7.3.

Does the sequestering agent drop it even more? Or should I drop the pH a bit before I start? Or test after all the ascorbic acid and sequestering agent are in and adjust pH up or down as necessary? In case it matters, I ordered ProTeam Metal Magic to use as the sequestering agent.

Sorry (again) to hear that the treatment didn't work well for you. Hopefully I'll be more lucky. The results from the test with the 1000 mg. ascorbic acid caplets were pretty amazing, as I mentioned before.

Thanks again for all your help, Gary

 

[chem geek]

Your pH should drop as the FC drops. In fact, you may get to 7.3 just from the consumption of 7 ppm FC alone. Then, the ascorbic acid will lower the pH from there. So I don't think you'll have any trouble getting down to a pH of 7.2.

As for the sequestering agent, I don't know how much that changes the pH. When I added mine, I didn't notice a change, but I did notice that the water looked a little dull the next day. I was worried it might be algae starting, though that didn't make much sense given the PolyQuat. It cleared up in a day or two so must not have been algae (there wasn't any chlorine in the water) and was probably something temporary associated with the metal sequenstrant -- I used a fairly large dose.

After almost a week, I added back chlorine slowly and it had chlorine demand as expected from the excess ascorbic acid in the water. The chlorine level held at some point and has been stable since (the water is now cold at 50F so chlorine usage is very low at less than 1 ppm FC per week in the covered pool).

 

[gtm]

Thanks Richard. I'll monitor the pH as the FC drops, but won't adjust anything until I see how it goes. I did some searching after reading your message for more info about the relationship between FC consumption and pH, but didn't have any luck. Would anyone happen to know if there's a thread on that topic that you could point me to for further reading?

 

[chem geek]

The chemistry behind the acidity of chlorine consumption is in this post, but it doesn't translate that into acid equivalent. In 10,000 gallons, a drop of 1 ppm FC has the same effect on pH as 1.5 fluid ounces of Muriatic Acid (31.45% Hydrochloric Acid). There is a small difference in TA between the two situations since every 1 ppm FC contributes about 0.1 ppm TA near a pH of 7.5.

In your 15,000 gallon pool, a drop in FC of 7 ppm has an effect on pH equivalent to 14.4 fluid ounces of Muriatic Acid. I use my spreadsheet here to figure these things out, but it's not easy to use.

NOTE: In my earlier post, I forgot to include your Borates. When I do that, I find that the using up 7 ppm FC has the pH drop from 7.5 to to 7.35 instead of 7.29, so with 1-1/2 pounds of ascorbic acid you'll get down to around 7.24 in pH. This doesn't have to be exact. Marie's instructions are just to prevent metal ions re-staining from higher pH. The lower pH helps keep them in the water until you add metal sequestrant. If one had high pH to begin with, then they should lower it first before beginning the procedure.

 

[gtm]

Hi Richard,

I've been working in the yard all day and just saw your reply. I did a quick scan of the link and I'm looking forward to reading it more thoroughly. Thanks much for sending that. At first glance it seems to be exactly what I was looking for.

Thanks, too, for the reference to your spreadsheet. I loaded that some time back, but I'm afraid it's beyond me. I'm mostly a Linux/Matlab guy and Excel (and Windows in general) tends to befuddle me.

FWIW I've decided to track (daily) the FC, CC and pH changes as the process unfolds. This is just for my own curiosity, but I'll be happy to post the results later if you think the data would be of any interest to you.

Thanks again for the link ... Gary