Green film especially after rain

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kmccomp

Member
Oct 20, 2019
10
Treasure Coast Florida
Hi, all. I let FC get away from me and found it low or 0 once or twice and then developed moderately green pool (4600 gal, above ground).
Results at that time (TF-100 kit):
pH 7.2
FC 2.5
CC 0.5
Alk 240
Hardness 525 (no control, it comes from the well that way)
CYA 30

My CYA was 30, so I maintained FC level between 12 and 16 for a whole week with 10.5% liquid chlorine. I also backwashed frequently when psi rose by 1 or more. That did a little to reduce the green color, but not happy with the progress, so I brought it up to over 20, then over 24, which finally turned the color from green to white and have maintained it over 20 since. I did more TFPC school reading and added brushing the walls to my twice-per-day routine of testing/adding chlorine plus vacuuming every couple of days. Most of the time chlorine barely drops by 1-3 ppm. I had been SLAMing for three weeks. I tried DE powder as described for three days, which helped clear up the white cloudiness significantly. I then got into a cycle of brushing, testing, adding chlorine three times per day.

Finally water was clear and sparkling (like drinking water), the morning's OCLT (Overnight FC Loss Test) was <= 1.0, and CC (combined chloramines) is always 0.5 or lower (I rarely ever see a higher reading than that.)
Results:
pH 7.5
FC 12.5
CC 0.5
Alk 190
Hardness 500
CYA 40

So, I started to let chlorine go back to normal. Two days of sun, all tests and clarity were good (FC still above 10), then one night of rain and boom – slight green color again on the walls. Now I’m in this cycle. The three ending slam tests become good, so I let chlorine go down and boom – slight green color develops again especially if we get any rain. It takes about 3-4 days for chlorine to go back down to normal (5-7), but it rains every few days. The pool is exposed to nearby Australian pines and an oak tree (I think), which is currently dropping its leaves. I clean out debris frequently throughout the day.
Current Results with slight white cloudiness:
FC 19
CC 0.5
CYA 40

Several users have remarked about issues with rain, but generally the responses have all been – keep slamming.
Thank you for reading.
 
Welcome to TFP.

After a rain when you first see algae what is your FC level?

Do you add liquid chlorine daily? What time of day do you test and add chlorine?

When it rains do you still test and add chlorine?
 
Thanks, ajw22. Here are my responses.
Q: After a rain when you first see algae what is your FC level?
A: As noted, FC has not even dropped back to normal limits, yet. Still above 10. In second paragraph, it was 12.5.

Q: Do you add liquid chlorine daily? What time of day do you test and add chlorine?
Maintain chlorine during SLAM. When pool is finally clear, check FC every morning, just after dawn.

Q: When it rains do you still test and add chlorine?
A: Yes. I test every morning.
 
Is your AG pool at grade or above grade? Does it get rain runoff into it?
 
It is above ground completely from bottom to top. There is no cover over the pool area, so when it rains, it gets rain water in it. The surrounding trees are not directly over the pool, but with a breeze, we get pine needles and other leaves into which it I clean out daily - sometimes multiple times a day on windy days or like this fall time of year when the items are dropping more regularly.
 
I think I may have misunderstood your last question. After I had a clear pool, the FC had been running consecutively at 12.5 (8am), 11.5 (9pm), 11.5 (8am), then next day at 8am it was 10 after an overnight rain and that morning is when I saw the slight green tinge on the walls. Today and tonight the white cloudiness has been dissipating pretty well. It poured 2" last night, but no rain today. I will update with new results from OCLT tomorrow. Thank you.
 
When you first see the green and before you raise your FC what does a Overnight Chlorine Loss Test show?

Are you following all the steps in the SLAM Process? It is more than just raising your FC.

Do you lower your pH before raising your FC to 16 for CYA 40?
 

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I do not do an OCLT every day if I have already passed the 3 SLAM tests. Also, the previous day before the rain, the OCLT did not drop - 11.5 at 9pm and 11.5 at 8am). So, then I only do an AM Chlorine check and hence, do not know what the OCLT would have been after the rain and once the green was noticed. The values given in last action were after completing the SLAM process with all 3 ending tests passing.

Yes, my SLAM process recently has been brushing, testing, adding chlorine three times per day, maintaining FC over 20, running pump 24/7, and backwashing as needed.

Yes, I lowed the pH at the beginning of the SLAM before raising the FC.

This morning's results.
FC 18.5 (previous night's was 19)
CC 0.5
I will keep FC >=20 with brushing, etc. until pool is clear. It is currently still slightly cloudy white.
Thank you.
 
It is possible you are seeing iron precipitating into your pool. Well water is the culprit.

Test your well water (not your pool water) for iron content.

The description sounds like algae but your attempts to remove it seem thorough........rain does not cause an algae bloom.....neglect does.

An iron test may be revealing.
 
We do have iron bacteria in the well water, but I would expect the iron to be brown, like it was when we filled the pool, not green. We used the clean, clear pool for two weeks, until we got the first rain and I noticed the green. I'm getting better at responding to problems. This week, the pool cleared up much faster and I think it will be clear again within a day or two. Could rain precipitate the iron again? And would it be green, not brown and the green turn to white after chlorine addition?
 
In much smaller iron concentrations, adding chlorine will turn the iron out of solution = green water.
I have that issue. Not nearly enough to turn brown (that would be super high) but just enough
that about every other year the water tints green after adding the first bleach on opening day.

If it is iron, you could try adding a few layers of polyfil to your skimmer and run the pump 24/7.
most of the time, the particles will collect in the polyfil.

But before you try that, see if you can get it tested at a pool store. The only time
it's recommended to use them for testing is metals because the drop test kit for it
is really spendy.
 
The "green to white" part puzzles me but everything else makes sense. Iron in your pool water precipitates into a yellowish brown substance when the rain locally alters the pH. The yellowish brown precipitate combined with blue pool water turns the water greenish. It's a very common phenomenon.

If you leave everything alone, it should go back to clear after a few days as the iron precipitate re-dissolves back into soluble iron.

I can't provide an explanation for the green to white but your description of what you have been doing makes me conclude it is probably not algae.
 
Sorry for the long delay; a lot going on the past month. It is getting cool here, so just trying to clear up the pool and cover it (lately only running pump 10hrs/day). All of whatever the recent green cloudiness is has settled out to the bottom. The rest of the pool water is crystal clear, so I need to be able to vacuum to waste, but currently do not have that option (lack of setup). My current vacuum (small Pool Blaster) sends the water back into the pool (along with all the fine sediment). My pump is only a 1050gal/hr, so not much pull power. Bought some accessories and hope it will help. Will update in another week or two. Thank you very much.
 
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