Just filled pool and water turned green after adding bleach

@richard 320,
Thanks for the quick reply and reference to the HTH metal sequestrant.
Iron in my tap water??? I've been filling the pool for 15 yrs with that water and never experienced this? Could it be metal contamination in my equipment (new heat pump, 15yr old filter, 15yr old super pump II) or winterizing products? I had a different pool guy winterize it last fall. Not sure what he used.
Also, note that my liner is sand colored, not blue. Therefore the green color is not necessarily due to yellow/brown staining.
I hear you about the pool stores but they're all I have at the moment. Getting decent tests kits is not trivial in Canada but I'm working on it.

I added sequestrant last evening and the water is pretty much cleared up now. There does not seem to be any visible staining on the white steps.

Don't know what ingredient was in the sequestrant (not specified on bottle) but it brought my ALK down from 80 to 40ppm and my PH down from 7.6 to 6.2 !!! That explains why any metal in the water was redissolved but since it is the first time I use that type of product I have no idea if such drastic acidifying is expected from sequestrant use. I'm rebalancing my PH now before doing anything else.

My question now is since there seems to be metal in the city water (despite 2 pool store tests, and the city saying otherwise), should I drain the pool before rebalancing and introducing bleach? What would prevent the metal from precipitating again as soon as I add bleach and/or raise PH?

Finally, is it possible I brought this onto myself simply because I did not wait long enough after adding my 3kg of baking soda before introducing the bleach? i.e. that the color change was strictly due to soda/chlorine interaction rather than actual metal in the water? I'm an engineer, not a chemist so I am intrigued and perplexed.

Thanks

@duraleigh, @IceShadow,

Thanks for chiming in.

Measured PH with:

1. HTH test strip
2. Titration using Phenol Red
3. Pool store

PH results varied from 6.2-6.5
TA was consistently 40-50
CH 80
FC, CYA and Salt close to 0ppm

I also contacted the city water treatment facility and they confirmed iron and copper in a city water sample should be undetectable (0ppm) to the usual pool water testing methods, unless my plumbing is contaminated.

That leads me to believe metal was not the issue. Its never been in 15 years with this pool, filling it from the same municipal water source. Anyway, we will see as I re-balance the pool water. If it turns green again as I raise PH/TA and FC, I'll be pulling out whatever hair I have left

Planned actions:

1. Just added half the calculated (PoolMath) dose of soda ash to bring PH (and TA) up.
2. I'll retest in 1h and add the remaining required dose of soda ash or switch to baking soda according to PH/TA results.
3. Once PH and TA are on target, I'll add 10% bleach to bring FC up to 1ppm only. I'll then give it 1h.
4. If I don't see any yellowing/greening of the water, I'll retest the water and take FC up to 3ppm
5. I'll wait another hour with FC at 3ppm, monitoring for color change.
6. If all good, I will put in the salt and CYA, wait until tomorrow, then fire up the SWG.

Comments welcome.

@Maddie,
Well, I'm just going by the PoolMath (and Water Balance for SWGs - Trouble Free Pool) recommended ranges. It's been working out great for me so not looking to change a winning strategy. Why do you think a TA of 60-80 is too high?

@duraleigh,

You are absolutely right about the Phenol Red test having a lower limit of 6.8. I just interpreted the "Yellower than 6.8" result I got as consistent with the HTH 6-Way test strip and pool store results of 6.2 and 6.5 respectively. You are also absolutely right about my current testing being less than ideal. However, those are the tools i have readily available to me. Not ideal, I know but they have kept me out of trouble... until now. I have a local industry contact (via pool store) looking into getting me access to a decent Taylor kit. Here in Canada, they appear to be unavailable for retail. Not holding my breath though.

No, not exaggerating about the 30 minutes for the color to start turning. OK, maybe it was 40 but definitely lime green within the hour.

I understand from some of your previous posts that you are a water testing professional so I will take your word on the iron content in my pool. I hear you about the iron in the pool not being detected after the water turned green because it was oxidized. I don't understand the details but defer to your expertise. That said, since I had both the pool and hose water tested separately, and they both tested 0ppm iron and copper, I have to assume the iron came from my pool equipment rather than from the tap (iron not oxidized in that sample, and tested in 2 different pool stores with 0 ppm results).

I've never had to raise TA by a lot in 15 yrs. This year's 3kg baking soda addition was a first. Maybe my delivery method was flawed and leached out iron from my equipment? I essentially bypassed the heatpump and salt cell (assuming my check valves work), set the filter to recirculate, and added one 500g box of arm & hammer at a time into the skimmer. Can that leach iron out of the pump and filter? About 30 minutes later, I added 5l of 10% bleach in front of the deep end return. The color change started shortly thereafter.

So, should I keep up with the re-balancing steps outlined in my previous post or would you recommend I drain this iron tainted water and start over with a fresh fill? My PH and TA are currently back to normal and I was waiting for the sun to set before adding bleach.

Thanks!

@Maddie,
Typo. I should have written 80ppm.

No negative connotation intended at all @duraleigh. I appreciate your help.

Starting with a clear pool ( PH, 7.4, TA 80, FC 0 ), I tried raising FC to 3, slowly adding 10% bleach in 2 doses of 1000ml, waiting 1 hr and testing FC between each. The water started turning green again. I'll give it 24-48 hrs, keeping FC at 1-3ppm with bleach and see if it clears up. Don't understand how getting the water tested by 2 different pool stores, when it was green and when it was clear shows 0ppm iron. Same for the fill water.

FC down to 1ppm around 4pm today. Pool still greenish but getting lighter. Did a backwash and the water in the waste line sighting glass was brownish/yellow. It took about 2 minutes for it to turn clear. That seems to positively confirm the presence of iron despite test results showing 0ppm iron (you were right @duraleigh). I raised FC back to 3ppm and will backwash again after 24 hrs. Looking out the window, the bleach addition to 3ppm has already darkened the green tint in the water. I plan to do another shock/sequestrant cycle after the next backwash tomorrow. If a few cycles of that still results in green water and brownish/yellow backwash water, I’ll have no clue what to do next.
Is it possible I have iron contamination in my pool filter itself ? A vacuumed up bolt or other metal debris stuck in there from last season?

I think I've solved the green pool "mystery". I'll wait 24-48 hrs to confirm then I'll report back on the details to hopefully save others the trouble if they find themselves in a similar situation.
SgtWilko

PROBLEM SOLVED!

The problem: While opening the pool after a liner, stairs, skimmer change, the water turns green every time I add chlorine. Fill water is city supply. PH and TA are in range. Nothing else added or adjusted yet. No detectable iron or copper in the fill water or pool water.

The short version:
It appears there was some foreign metal object lodged somewhere in the system. Probably when closing the pool last fall or when replacing the steps (piping to step jets) and skimmer before opening the pool this year. After about 5-6 cycles of shocking the pool (turning the water green) / filtering for 24hrs / backwashing... adding bleach and raising FC to 5ppm no longer turned the water green. The assumption is that the metal was completely oxidized and filtered out at that point.

The longer version:
The unverified theory (as suggested by @duraleigh) is that metal tests at the pool store could not detect oxidized/precipitated iron in the water. That's why these tests always came back negative. There is no significant iron in the fill water (confirmed by the city) and no iron in the pool water unless I add bleach, which oxidizes the foreign metal bits stuck in the system. This oxidized metal is drawn into the pool water, making it take on a yellowish-brown tinge. which combined with the liner creates the green water color. The oxidized iron was obvious when backwashing as the water in the sighting vial would start clear, then change to a clean and clear yellow/brown for about 90 seconds, before running crystal clear again (video here). After running enough shock/filter/backwash cycles, the stuck metal bits were completely dissolved and filtered out. Adding bleach no longer turns the pool water green. Note that I used sequestrant only once, the first time the water turned green, but that did not prevent the water from turning green after each addition of bleach afterwards. It probably has helped the filter retain the oxidized iron more effectively but I'm speculating.

Pool is now fully balanced, SWG is started and water is beautifully crystal clear.

Hope this helps anyone else plagued with a "mysterious" source of iron in their pool water.

It would be interesting to hear from one of the more chemically knowledgeable people on this forum (@chem geek ?) on this "theory". In case the above is all hogwash and the reality completely different. I want my sharing this mishap to inform, not misinform.

Sgt Wilko