My ascorbic acid adventure

anthony21078

Well-known member
Jun 14, 2018
90
Long Island NY
Opened the pool 2 weeks ago and noticed that the liner had a lot of yellow staining on many different areas. Confirmed with vitiamin C that the stains were from iron.
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vitamin C in sock test

Here is the order in which I proceeded
Saturday 5/4/19
1)Dropped FC to almost zero with a neutralizer
2)Dropped the PH to 7.0
3)Filter on circulate
4)Added 16oz of Kemtek 60% algeacide
5)Added 1lb ascorbic acid. Waited 30 min but didnt see any stains lift
6)Added another 1lb of ascrobic acid and over the next 30 minutes and all the staining was gone.
7)Added 2 quarts of Metal Out by Pool Mate
8)Filter back on filter mode.

At this point it was around 9pm but the pool was extremely clear and the liner was bright blue.

Sunday 5/5/19
At 9am the pool had turned light green which I read was from the iron being held in suspension by the sequestrating agent (Metal Out). Even though I knew this was supposed to be normal, it was rather discouraging and frustrating to go from blue to green over night. The CYA levels in my pool were over 100 from using pucks so I figured this was the best to time to do a partial drain/fill and also get rid of some of the iron in suspension. Filter was set to waste with only the main drain pulling water. Over the next few hours I began to brush the sides/floor while pushing the debris to the main. My pool was a little dirty but even when I would brush the clean sections, you could see a darkish green cloud form. I brought the water down to roughly one foot in the shallow end.

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Monday 5/6/19
Filled the pool overnight and woke up to this today. FC was still at zero and PH was at 7.0. It took 3 gallons of 10% slowly poured over 4 hours to bring the FC to 3.0. Bumped the PH to 7.2. TA is 150. CH is 200. Currently there are no more yellow stains. The steps are free of yellow staining as well. I can only hope the clear water stays like this.

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Last edited:

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,216
Tucson, AZ
Just a note - ascorbic acid is a chlorine neutralizer and so there’s no point in using a separate chemical. You would simply add more AA.

Have you had your fill water tested for iron? That is a very likely source.
 

anthony21078

Well-known member
Jun 14, 2018
90
Long Island NY
Just a note - ascorbic acid is a chlorine neutralizer and so there’s no point in using a separate chemical. You would simply add more AA.

Have you had your fill water tested for iron? That is a very likely source.
Well my FC was over 8 and I don't know how much ascorbic acid was needed to drop it to zero. But seeing how 5lbs of chlorine neutralizer was only 13.99, it was probably the right choice since ascorbic acid was 19$ for 2.2lbs.

I didnt test the fill water but I did take a pool water sample before I started this process to the pool store and it tested 0.1ppm for iron.
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
14,437
Evans, Georgia
You're not using Clorox XtraBlue pucks are you??? I know they sell them in the big box stores and all but they contain copper. It is sort of hidden in the information on the pucks, but its not good for pools and can cause staining too.

Maddie :flower:
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,216
Tucson, AZ
Well my FC was over 8 and I don't know how much ascorbic acid was needed to drop it to zero. But seeing how 5lbs of chlorine neutralizer was only 13.99, it was probably the right choice since ascorbic acid was 19$ for 2.2lbs.

I didnt test the fill water but I did take a pool water sample before I started this process to the pool store and it tested 0.1ppm for iron.
A rough estimate is that it takes 2.5 parts AA to reduce 1 part of chlorine in water. So in your 22,000 gallon pool, you would have needed an additional 3.67 lbs of AA to reduce the 8ppm FC you had. Based on your cost, that would have been $32 more for the extra AA or $18 more than what you paid for the neutralizer. Chlorine neutralizer is typical sodium thiosulfate which is cheaper to manufacture and sell than AA but it does leave sulfates behind as a byproduct. In your case of a one-off treatment, that’s not a big deal but sulfates can damage SWG’s and so people with SWGs should avoid sulfate exposure as much as possible.

Iron is very difficult to get a good measure on because most pool stores don't test for it correctly. In a pool like yours, very little iron is going to exist as soluble iron (the kind most easily detected) because the chlorine has already oxidized it to its insoluble, precipitated form, ie, the stains. So unless a water sample is treated to take any precipitated iron and convert it back to soluble iron, the test will always show low iron.

The best, and more expensive way to know, is to have a fill water sample analyzed by a commercial lab that tests drinking water. Those labs can give very exact results. People with well water will often do that to determine drinking water quality.
 

anthony21078

Well-known member
Jun 14, 2018
90
Long Island NY
I just started to notice some of the staining re-appearing on the liner. Confirmed it was iron again with a few vitamin C pills. I’ve been testing the water everyday (FC and PH) and everything else every 4 or 5 days. Since the ascorbic acid treatment in early May, the PH was holding at 7.2 for a week and then moved up to 7.4 for the past 2 weeks. I just noticed the staining today and the PH was 7.8 and yesterday it was 7.4. It did rain last night but it has also rained at least 3 times a week in the month of May so I’m not sure how the PH made that big jump in roughly 12 hours. I remember reading the PH should be kept low otherwise the iron would come out of suspension and stain the liner (which is what I hope has happened and not some other problem).

One day after the first ascorbic acid treatment the water was green from the iron in suspension and since my CYA was also over 100, I did 2 partial drain/fills bringing the water down to about 12 inches in the shallow end of my 22000 gallon pool each drain/fill. I can’t be sure of how much water was removed but I think it’s safe to say around 1/3 each drain/fill. After the pool was filled the second time, the water was clear, the liner was clean and the CYA was around 50.

The sequestering agent I used was Metal Out by PoolMate and I have not added any since the initial treatment.

So my question is this;
Is it more likely that since I partially drained/filled the pool twice post-treatment, I obviously lost a lot of the sequestering agent and adding new water (which may have iron in it) caused the stains to re-appear but just took some time?

Or the high PH of 7.8 caused the stains to come back in literally one day?

Also, I recall reading that in addition to keeping the PH on the low side to avoid the stains to re-appear, FC should be kept low also. Right now my CYA is 40 and I have been keeping the FC on the higher side of the recommended range which is usually around 6. Is it better the keep the FC at maybe 4 or would it help to raise the CYA a bit? Now that the weather is getting better and the sun is out much more, Im losing approximately 2-3ppm of FC each day during sunny days.
 

pooldv

TFP Expert
Platinum Supporter
LifeTime Supporter
Moderator Emeritus
Aug 10, 2012
25,412
FL panhandle
Raising CYA will reduce your daily FC loss. Keeping FC in the middle of the range should work fine.

You are correct in both cases, higher pH can cause stains to recur and draining will dilute the sequestrant which can also cause stains to recur. Keep an eye on the plastic components in the pool, stairs, skimmers, etc for stains. Plastic items tend to stain first. Add sequestrant as soon as you notice stains recurring.

Your TA is a bit on the high side which will push pH up. Lowering your pH regularly will slowly lower your TA which will reduce the upward pressure on the pH.
 

anthony21078

Well-known member
Jun 14, 2018
90
Long Island NY
Raising CYA will reduce your daily FC loss. Keeping FC in the middle of the range should work fine.

You are correct in both cases, higher pH can cause stains to recur and draining will dilute the sequestrant which can also cause stains to recur. Keep an eye on the plastic components in the pool, stairs, skimmers, etc for stains. Plastic items tend to stain first. Add sequestrant as soon as you notice stains recurring.

Your TA is a bit on the high side which will push pH up. Lowering your pH regularly will slowly lower your TA which will reduce the upward pressure on the pH.
Water test this morning after adding more sequestrant yesterday and ciruclating the water overnight;
FC 0
PH 7.0
TA 120
CH 150
CYA 50

Added 30oz soda ash after this test and the ph is 7.2. I just read that borax is probably better for my situation since it doesnt raise TA as much as soda ash? Starting to raise FC now.

Ill attempt to aerate with the return jets (assuming the jets will do the job) and monitor TA and PH over the next week. I do not want my PH to go higher then 7.4 to avoid the staining from re-appearing so Ill test the PH daily and reduce it as need be.

Question....during the aeration process, do I need to allow the PH to jump higher then 0.2 increments before I lower it again (example, 7.2 to 7.8)? Or can I lower the pH as soon as I see an increase?