Ascorbic Acid Treatment for Metal Stains in Vinyl Pool

MichiganBruce

Member
Jul 1, 2019
5
Midland, MI
I followed the process for identifying and then treating iron stains on my vinyl pool, as laid out in the TFP Forum thread here;

as well as another detailed version of the same process on another forum here;

I used about 1/2 lb of ascorbic acid per 10,000 gals, then followed up with the prescribed dose of Jacks Magic Pink Stuff as the sequestrant and CuLator metal eliminator in the skimmer. Initially the results were very good (stains removed) however as I slowly brought the pH back up to the 7.2 level the stains started to re-appear. Following the guidance, I reduced the pH and added more sequestrant, which seemed to reduce the staining. I then started to bring the chlorine level up, but kept it on the low side, and did not shock the pool. As I got the chlorine stabilized, I kept the pH on the low side (6.9-7.1). I let the pool run like this for several weeks, and all seemed to be stable. I then brought the pH up to 7.3 over several days using Borax (because the Alkalinity was already on target). This was about a month after the initial AA treatment. Then I shocked the pool for the first time, using granular Super Shock at a level of 1 lb per 10,000 gallons. Following the Shock, the pool bottom is now almost completely covered with the light brown iron stains again. (Makes me want to scream!) It seemed that the process was going well and according to plan.

I'm looking for input on what happened, and what the best course of action is.

I'm hesitant to start the process over again, since it's now sunny/hot and algae is a real concern if I let the chlorine drop (it was May in Michigan when I did this AA process initially). I suspect I will need to reduce the pH and add sequestrant, but I'm hesitant to continue swinging the chemistry (and throwing money into the pool water) until I have some guidance from other more experienced pool users who have been down this road. I'm happy to fill in any details of my process that I may have missed.

Thanks for your input.
(18'x38', 30,000 gallon vinyl lined pool)
 

Texas Splash

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Jun 22, 2014
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Welcome to TFP! :wave: I see two concerns with what you described:
1 - Why did you do a shock treatment? Do you have algae?
2 - It's possible your iron content is so high that your water is exceptionally sensitive to pH and chlorine which might make it very difficult to manage. In cases like that, a LOT of pre-filtering is required and/or having fresh water trucked-in is usually the best option.

Can you confirm which test kit you are using? When you do get a chance to update your signature, please include that you are on a well, and which test kit you are using.
 

JulieMorris316

Well-known member
Jul 21, 2017
58
McIntosh FL
I can’t really answer your questions about the AA treatment process, but I also had iron stains on my fiberglass pool. It was enough that there was a fairly decent brown tint to everything under the water level. I tried AA once, but I live in Florida and dropping the chlorine for long enough to do the treatment didn’t go so well lol. I ended up using a product called Metal Magic by Proteam and it cleared them up. For me it was the best option since you don’t have to lower the chlorine levels to use it. Just dump it in and brush the walls fairly often until the stains have lifted. It does work a lot slower than AA, but the stains don’t come back for a good long while, and I use a maintenance dose once I start to see any trace of them and it clears them up. I’m not sure how true it is, but it’s supposed to be one of the only products that precipitates the metals so the filter can catch them, and I always have a good amount of white powdery stuff on the filter afterward that needs cleaning off, so whether it’s the metals or not, it’s causing something to clump... just throwing it out there in case it helps!
 

MichiganBruce

Member
Jul 1, 2019
5
Midland, MI
Texas Splash - Thanks for the feedback.
1) I shocked the pool for two reasons; TCL was getting to be a bit higher than FCL, and I was getting some yellow algae. I understood it to be a normal maintenance practice to periodically shock the water when TCL gets higher than FCL.
2) The staining does seem to be very sensitive to water chemistry. Prior to the full coverage staining that I now have, I could see the staining increase as I brought pH up and with increase chlorine levels.

We are not using well water, and I have not measured iron content in our city water. It seems that the only source of iron would be the pool heater core??

My regular test kit is the Lamotte ColorQ. I have nothing to compare this to (except the occasional test strip) but it seems to work well.
 

MichiganBruce

Member
Jul 1, 2019
5
Midland, MI
JulieMorris316 - Thanks for the suggestion. I am open to try the Metal Magic, but I'd like to get some input first on the root problem, so that I'll have some idea if this product could help my situation.

As you mentioned, mid-summer is not the ideal time to drop the chlorine level in the pool to run the AA process.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
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Texas, San Antonio/Marion, South-Central Area
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Good info. So I can tell you this:
- The Lamotte provides some fair results, but has its limitations. We would encourage you to obtain one of two kits - see Test Kits Compared. The TF-100 is my choice (w/ speedstir if you can).
- Heater cores typically have copper, but also some local water supplies simply have higher levels of iron.
- Shocking weekly is typically a pool store myth (routine) that is not required as long as the water is maintained properly throughout the week.
- No question though, if you have algae of any type, the algae must be eliminated via the SLAM Process before attempting to resolve any metal staining. Once the SLAM is complete and verified by passing all 3 criteria, then the pool can be treated for staining.

You have what, 2-3 months left in your swim season? You might consider tackling the algae now and just let the staining ride until fall. Then once the water temp falls to 60 or below you'll have a better change of managing the AA process with the very low FC level and avoiding an algae bloom during the AA process. Just a thought.
 

MichiganBruce

Member
Jul 1, 2019
5
Midland, MI
I eliminated the algae with a SLAM dose of liquid chlorine. Chlorine level is still high in the pool but coming back down. At the high chlorine levels I found that my alkalinity value and pH measurement both dropped, but I suspect these are not accurate due to the high chlorine so I have not reacted to these. Should I try to manage alk and pH now or wait until chlorine has stabilized?

It is reasonable to do the AA process in the late season just before shutting down. I have done this before. I thought I was getting ahead of it this year by running the AA process right after I opened the pool. I get the merit of the suggestion, but I really hate the idea of ignoring the staining for a few months, since it makes the pool look so bad.

Also, I'm not sure I understand the root cause of the problem, or how to keep the staining away once it's gone.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
31,460
Texas, San Antonio/Marion, South-Central Area
Pool Size
17888
Surface
Fiberglass
Chlorine
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SWG Type
CircuPool RJ-45 Plus
You certainly can do the AA process now if you wish. Just follow those directions. But keep in mind ........ the SLAM "dose" you noted above may not have been the complete SLAM Process which can take several days to work and pass by maintaining that SLAM FC level consistantly. So just make sure that you are clear of any algae before starting the AA process. If in doubt, you can always do an Overnight Chlorine Loss Test.

Once you get to the point where algae is no longer an issue and the staining has been resolved via AA, preventing future staining boils-down to these basic concepts:
1. Ideally repacing iron-saturated water with fresh water. When not possible, eliminating additional iron from entering the pool either by pre-filtering or getting a new (fresh) water source
2. Utilizing a good HEDP sequestrant consistantly to keep the iron in a solution state
3. Keeping the FC from increasing too much from your ideal target range; see FC/CYA Chart
4. Controlling the pH and keeping it on the lower end of the spectrum if possible - being careful about corrosion to equipment (i.e. heater core).
 

MichiganBruce

Member
Jul 1, 2019
5
Midland, MI
Just to make sure I understand the SLAM process. Should I be trying to balance other factors now (such as the slightly lower alkalinity or the low pH) or wait until the chlorine level has stabilized and is within the target range?

FYI. My current chem levels as measured by the ColorQ;
FCl: Hi
TCL: Hi
pH: 6.9 (it was 7.3 when I started the SLAM)
Alk: 53 (it is bouncing around between 53-85. Was 134 before SLAM)
CH: 201
CYA: 50
Temp: 84

I have a DPD-FAS test kit but the reagents are expired. With expired reagents I got a TCL reading of about 20ppm chlorine, and it's a week since I added the high dose of liquid chlorine. The pool was covered while we were travelling last week so the chlorine didn't burn up very fast. It also looks like I still have some yellow algae in the pool (unless the yellow/brown powder like substance is something other than algae).

Just a note on how I manage chlorine level. I have an in-line chlorinator using 3" tabs, and even with the chlorinator dial turned down very low the pool chlorine levels tend to run high. The chlorinator manufacturer says my system back pressure is too high allowing too much water head in the chlorinator (my trials at fixing this could be a whole new post). The most effective way I have to get chlorine down to the target level is by not running the pool pump 24/7. I had been managing chlorine in the 3-5 ppm range by running the pump 18 hrs per days. However since I SLAMmed the pool, and we were out of town, I was running the pump 24/7, and just backed it down to 18 hrs a couple days ago. I'm surprised that the chlorine is still so high.

At this point I need to get rid of the algae (if that's what it is) and get the chlorine level stabilized at a lower (and measurable) level. Then I will worry about the other chem levels.

Any other advice is appreciated.
 
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