Water turning green with Chlorine after stain remover but no iron in pool

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Fab_974

Member
Jun 18, 2024
5
Montreal - Canada
Hi!
I have been struggling with green water in my pool for days and spent a lot of money at pool stores to buy products that do nothing.
I have read this great forum post but it does not address my issue I think: Pool turned green after using StainFree

I have a 30,000L fiberglass pool that is 3 years old. My current levels are:
FC: 0
TA: 130
CH: not measured recently but likely around 300 (I want to bring it to 450 when this situation is solved)
CY: 40
PH:7.8
Salt: 3300ppm

I had light brown stains on my walls caused by a PH above 7.8 according to the manufacturer. He told me to use a stain remover (citric acid) while having my FC at 0 which I did.
When I increased back my FC, the pool became green right away. I thought it was from metals oxydation.
So I had my water analyzed at a pool store and there is no iron or copper in the water.
Could it still be iron but so low that the machine can't detect it? Or what else can it be?
Where would the metals/iron come from? My heat pump is titanium and I don't think municipal water I used to fill the pool has iron in it.

The water is very slowly becoming lighter green (after a week). I am thinking it is because FC is going back to 0 but I can't keep my pool at that level for so long when temperature is above 80F . Assuming this is iron, is it getting lighter green because iron is deposited again on the wall?
How long does it usually take to be able to put back Chlorine to recommended levels? Is there something to do to accelerate this process?

Thank you so much for your help!

Screenshot 2024-06-19 at 12.04.37 AM.jpg
 
Welcome to TFP, It is a great site. I am not an expert especially on iron but will ask a few questions that will help some more knowledgeable people step in and help you. How did you test to get the numbers above? If you are using strips or taking to sample to pool store they are not valid in my experience. You need a TFP kit or Taylor kit especially for FC testing. do you use well water to fill or add water to your pool? What type of filter do you have? If it is cartridge filter have you checked since pool turned green? What product do you use to add chlorine to your pool, liquid chlorine, SWG, Trichlor tablets, ect. ? If you go to your profile then signature you can edit your signature to what your pool is, it helps the troubleshooting process. FC at "0" does not take long for algae to bloom. but iron also can cause it to turn green. you can DIY a filter to filter out Iron with a 5 gallon bucket and polyfill. you can search that on this site. but getting a proper test kit and good numbers are the start.
 
Welcome to TFP! :wave: It's starting to look like you might have both iron and algae. Regardless, you'll have to treat for algae first, and if there is iron, it's going to make it angry with the elevated SLAM FC level. SLAM is the SLAM Process we follow to remove algae. It works, but you must have a proper test kit. You should look into the Taylor K-2006C up there since they have proprietary rights to sell up north in Canada. If you have a way to pick up mail in the US, the TF-100 or TF-Pro series test kits are outstanding and a better value IMO. But you MUST have one of those ASAP.

For now, just add one gallon of liquid chlorine to the water each day. Don't try to do anything else without the kit, and stay out of the pool store. If you're not careful, the advice and junk they sell will make your situation worse.
 
If you do have shopping options, here's a good article.

www.troublefreepool.com

Swimming Pool Test Kits Compared

What pool test kit should I buy? Why shouldn't I use test strips? Our recommended test kits will pay for themselves in no time!
www.troublefreepool.com www.troublefreepool.com
 
Thank you all for your answers! This forum is fantastic and members are so kind and helpful!
I updated my signature with more details as recommended.
So for now I am testing my water at a pool store but will definitely change based on the suggestions received here.

This morning, after days of going lighter and lighter green, and having the swg off, the pool is back to blue. The water is very clear. So I think it rules out algea and confirms iron.

A few other comments or questions based on the thread:
  • I will get the Taylor K2006-C test kit, but I don't think it measured metals in the water. Do I have to rely on the pool store for those measures or is there a better way?
  • On 5 different occasions, I tested the water (at the store) and it had no iron or other metals. Could something else cause the water to be green like this (except algea which I don't think I have)? Or is it really the only possible cause?
  • Assuming it is iron as it seems the most likely, are the metal remover product efficient? Or it just precipitates iron so it no longer reactes will Chlorine but it is still in the pool and next time I use a stain remover it will come back ?
  • Is the stain remover (citric acid) what caused iron to be in the solution? My pool walls are white fiberglass but had stains (very light brown/orange/grey, hard to tell) but according to the manufacturer it was from high ph, not metals. Are there better ways to remove stains than those stain removers (which worked well) that seem to cause issues afterwards?
  • Should I add the one gallon of liquid chlorine per day while keeping the salt generator off? Or can I just turn the generator back on?

Thank you!
 
Taylor K2006 Kit does not test metal, so I would use a pool store for metals but be very suspicious as to accuracy of results, as I think you are by bullet point #2. Metals and algae are the 2 reasons for green that I know but Pat (Texas Splash) would know more than I do on that subject. Since your FC was taken to zero there is a good chance you have algae starting even if it was not the reason for the pool turning green so I would Slam the pool once you get the kit. To remove iron using polyfill, which is probably safest way to remove it, you can search this site for "how to remove iron from pool" it should return threads on how to make your own and you can start using it to remove the iron so it does not re-stain the fiberglass. As for turning on SWG; it won't hurt the SWG but then we do not know how much chlorine it is putting in the pool. If it were me I would do it and see if pool continues to improve, if not, turn it off and use gallon per day (Pat may disagree, listen to Pat, he knows more than I do). I assume your salt level reading is from your SWG and 3300 is within the normal limits but check with your manufacture to be sure. 40 CYA is low for SWG but from what I have read it does not hurt to run SWG at lower CYA levels (normal is usually 60 -90) but the sun will eat faster than you produce it. Again Pat may have a better insight. By the way do not add CYA to pool yet for 2 reasons; 1) may not be accurate then you put too much in 2) it is much easier and takes less chlorine and less testing reagents when slamming at lower levels, which translates to less money and work. Also, Taylor does have a salt testing kit, I bought one but do not use it, I use the reading from my SWG. Also you may want to start reading the directions or looking at videos on how to use the kit to perform different tests as well as SLAM procedures. We like pics of the pool to see how water is doing also.
 
I wanted to report back here to help others. I had only a few days to find a solution as I was leaving for a few weeks.
I tested first with an AA tablet on a stair and the stain vanished immediately. It was quite amazing. I have included a picture and you can see the white area where I moved the tablet. So this confirmed that 1. it was iron and 2. you really can't trust pool store results on iron levels as they repeatedly told me I had no iron in the water.
I wanted to do the polyfill procedure to really remove the iron from the water but did not have time before leaving so I went with the sequestrant route for now. I also could not procure AA easily so I bought a stain remover (picture attached) which does not list ingredients but I would assume it is citric acid.
It worked well as well within a few minutes and then I added the sequestrant which I will have to add for the rest of the season on a weekly basis.
Over the next 7 days, I kept my PH around 7.2 and poured daily liquid chlorine as I understood from the AA procedure on TFP that you need to consume the citric acid first before being able to bring back up your FC level with the SWG.
After those 7 days, I brought back up my levels to the TFP recommended ones. You can see the water is really nice now!
Once thing in the AA procedure that shed some lights for me is this sentence:
High ph along with high chlorine will precipitate any metals that are not sequestered out of the water and on to the surface of the pool again.
Click to expand...
The manufacturer always told me to keep my ph at 7.0 or 7.2 (which makes having the right CSI impossible) and explained to me I would get stains starting at PH 7.6 and above. But this is wrong and I finally understood why I had stains (iron) when my Ph was higher (but to the recommended range in fact).
Thank you again everyone for your advice!
 

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I don't know where the iron could be coming from. I had a pergola installed near the pool but it's aluminum so I don't think it's from this.
That leaves me with a few possible causes but I don't know which one is right:
  • Municipal water in Montreal
  • Rain
  • Pavers around the pool (maybe they contain some iron that dissolves through time)
  • Polymeric sand for paver joints (I can't find online if they contain iron)
If anyone knows about pavers or polymeric sand containing iron, I'd love to know!
 
You may want to contact the city. I looked at Montreal's web site, but the general water supply information is pretty generic. If you can contact one of their staff in the water department, they may be able to share with you latest test results. They do note that repairs can genereate sometimes significantly noticeable amounts of rusty water - you' see that, but perhaps not at lower levels. You could ask about having them individually test your water, or where they advise it be done.
 
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Sande may be right, and while your Muni water now and at time of testing was low in iron, when you filled your pool it may have been high due to some repairs/cleaning that was being done at the time, I think many of the pipes of municipalities that supply the water are made of iron. Good news is there are some fairly inexpensive ways of dealing with it.
 
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