Went away for two days and the pool went green. I think I know what went wrong, I hope..

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Skenn81

Skenn81

Well-known member
Apr 23, 2018
372
Florida
So yeah, I think I know what I did wrong but I figure I would post here to confirm my suspicions.

Pool details in sig, using the standard TFT test kit. Pool enclosed by a screen.

Before I left I took a full panel of readings, I had been maintaining my CL at 7 with a CYA around 50. The CYA had dropped to 30 so I brought it back up. CYA as of this post is at 60.

Here are the full readings:
CL: It was 2 when I got home and took the test tonight. I just added enough to bring it up to 24. Pump is going to be running 24 hours now and I will be checking the levels to keep up the target SLAM as much as I can. I will check it again late tonignt, first thing tomorrow morning, and just keep this going.

CYA: 60
pH: 7.4
TA: 70
CH: 290.

Pool has been wonderful for over a year, thanks to this website, and I have been in a great routine of testing twice a week, adjusting based on the calculator, and living a happy pool life. New filter cartridge purchased last Sunday and swapped out.

Went away Wednesday afternoon. Did my final test before I left, brought CL up to 7 with liquid, drove away. Drove home a couple of hours ago, pool went from clear to green. Took the readings, CYA still at 60, CL was at 2. I am not concerned with the CYA at 60 as I will just maintain at a higher level. The Florida summer heat and sun will bring that back down to 40 in a couple of months anyway and the rain is so much that I usually need to drain a few inches off the pool every couple of weeks. When I moved in the last owners had it way over 100 and I was able to keep the pool perfectly blue until tonight. Been following the TFP methods without fail for over a year and have had zero issues. Except when I had an issue. Meaning now.

I opened up the skimmer just to check. Half a dozen wiffle balls were in there. I noticed the surface of the pool, despite being green, had a bunch of bugs on it. Would this be the cause of the green pool? A lack of circulation for the past few days? The pool jets have been running on the same schedule now for 8 or something months, the pool vac just cruises around the bottom for his 4 hours a day, pump turns on at 7:30 and turns off at noon.

I dont know what else would have caused the sudden outburst of green so I am hoping it was this.
 
CYA 60 has a minimum FC of 5. Once your FC drops below 5 algae can grow. Your FC probably dropped from 7 below 5 in a day.

Put some trichlor pucks in a floater when you go away like that.
 
How do you typically add chlorine to the pool? Liquid Chlorine? With the FC at 7ppm when you left, it was probably barely above minimum of 5 when the day was over. Two days below minimum FC isn't good and would cause the algae to get ahead of you. But in my honest opinion, a clear pool won't go green in 2 days. The pool likely had a bit of algae from being at the lower end of FC. Then 2 days below and it broke loose and turned green.
I'd recommend doing the SLAM process as you indicated. Then keep FC closer to the higher end of the target range based on your CYA. No need to squeeze by at the bare minimum FC.

Live and learn. Keep us posted of your progress if you'd like.
 
I add only add via concentrated liquid.

So I was going off the usual chart: Chlorine / CYA Chart - Trouble Free Pool

Except under the assumption my CYA was at 50. Last weekend I did my monthly CYA test and saw it had dropped to 30. I added with the assumption it was going to be raised up to 50 but when I checked tonight i saw it was up at 60. I have been maintaining CL at 7 since January with no issues. I only check twice a week, Sundays and Wednesday and it has been perfect the whole time.

So with 50, cl at 7 is right in the middle of where the levels should be. At 60 I am suddenly at the low end of that chart.

So it was not the wiffle balls but instead I just screwed up with my calculations based on a lower than actual CYA level? Two days can send a pool into a tailspin this quickly?
 
Going 3 to 4 days starting with a FC of 7 is too long. Your FC would likely drop below minimum and algae would take hold. It can be invisible but waiting in the water and accumulating. Eventually you get an algae bloom which you did.

The FL sun uses 2-4 ppm of CL a day. You have to check FC every day or two to keep it above the minimum.
 
Skenn81 said:
So it was not the wiffle balls but instead I just screwed up with my calculations based on a lower than actual CYA level? Two days can send a pool into a tailspin this quickly?
Click to expand...
I doubt the wiffle balls were the culprit. They are round and probably let enough water pass to keep the pool mixed. Were any of the balls hard to remove when you took them out?

A pool won't typically go green in 2 days. It would first be cloudy and indicate something was wrong, but not be green. Don't get me wrong, I'm not judging, but just trying to help answer your question. It's likely you were at or below the lower limit of FC for a few days before you went away and those to extra days were enough to push the pool over the edge. Even a perfectly clean pool has algae in it. The target levels of FC just allow the FC to kill the algae faster than it can reproduce. Therefore algae levels stay low and no algae is noticed. It is only when algae has been able to overcome the FC and grow faster than it is killed will the pool turn green.
 
Obligatory photo from my return yesterday:

nrAicpH.jpg


Here is the update from over night. Before finally going to bed last night I brought the CL up a second time. From the initial shock it dropped down to 20 something. Got up this morning and just checked it again, it maintained throughout the night dropping from 24 to 23.5, which could just be a rounding error from doing the drops. I added another 10oz of cl and I will check it again as we get closer to noon. Filter is still running.
 
Okay so a few updates..

I went out earlier and brushed as much as the entire pool as I could reach. On the steps and shallow areas I watched the green algae billow off of everything and float away. I will post a new picture this evening.

I know the SLAM instructions say do not worry about pH as the levels will be unreliable during this process, but I tested it anyway just to see what is going on..

GQkweHY.jpg


The pH is currently at some incomprehensible level way beyond 8.0. Is that due to the chlorine content being so high and throwing off the readings or are there other things I need to worry about?
 

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Skenn81 said:
The pH is currently at some incomprehensible level way beyond 8.0. Is that due to the chlorine content being so high and throwing off the readings
Click to expand...
That is correct.

Did you test your pH prior to raising your FC to SLAM level?
 
Skenn81 said:
Okay so a few updates..

I went out earlier and brushed as much as the entire pool as I could reach. On the steps and shallow areas I watched the green algae billow off of everything and float away. I will post a new picture this evening.

I know the SLAM instructions say do not worry about pH as the levels will be unreliable during this process, but I tested it anyway just to see what is going on..

GQkweHY.jpg


The pH is currently at some incomprehensible level way beyond 8.0. Is that due to the chlorine content being so high and throwing off the readings or are there other things I need to worry about?
Click to expand...
Yes, when chlorine gets high, the pH is unreliable, hence the 1st step of the SLAM being "bring pH to 7.2".
 
So I may not have tested the pH during the panic moment of realizing my pool had gone green and I needed to start the slam. The pH was tested Wednesday though so not that long ago, but yeah, I missed that step which is on me.

Regarding the pressure on the filter, with the new cartridge the pressure reading is currently at 5 psi. Water flowing, the Polaris is moving about, and the skimmer is sucking in water so all appears to be normal. Nothing to worry about there?
 
I am going to add pressure readings to my log now. New filter couldn't have caused this mess, right?

About the CL dropping in two days, if I had not gone away nothing different would have been done outside of noticing the green a day earlier. I have always checked the water twice a week and have never had an issue. For it to go bad this quickly does it mean I have kept things low for too long? CYA at 30 to 50 at CL of 7 should have been fine, right? I only raised the CYA on Sunday, so it has been 60 only since then and the CL was still at 7, which, while on the lowest end, was still within range. Only a couple days below was enough to go green?
 
You are saying that you use liquid chlorine to chlorinate, but only add it once or twice a week? Hard to see how that is possible in Florida.
 
Mid afternoon update: CL has dropped down to 18. So that is a 6 ppm loss from this morning. When SLAMing is this faster than usual CL loss expected? Lost .5 over night, lost 6 since this morning.

On a positive note the water quality is already notably improved. We have backed away from swampy green to a greenish blue now. The shallow end is now clear, the deep end still needs some work. Pump still running and I Just got back from the pool store with another 7.5 gallons of concentrated liquid.

mknauss said:
You are saying that you use liquid chlorine to chlorinate, but only add it once or twice a week? Hard to see how that is possible in Florida.
Click to expand...

Yup, ever since I started May of last year, I have it all logged in my spreadsheet. I could have just been running on borrowed time though. The cycle usually goes something like I check on a Sunday and bring it up to whatever my current target CL is, so since January 6th of this year that has been 7. I then check it again 4 or so days later. The CL at that point has dropped down to 2 or 3 and then I raise it back up.

M3iUziW.png


That's a snapshot of part of my log. The CL numbers there are what it is when I take the reading and then I add liquid to bring it back up. What I am reading is that this may not be frequent enough, especially during the summer months?

Someone posted something about algae behind the light, I have never checked or cleaned there. I don't know how to take it off, is there something special you need to do so I don't get electrocuted or something? Power and water sounds like a bad combo.
 
For maintenance, You should be testing your FC and adding liquid chlorine daily. Eventually you might be able to test every other day but still add daily.

Keep your FC at SLAM level. It will fall rapidly as you are killing the organics.

Check your light. It should have a single screw towards the top of the retaining ring. Take out the screw. The ring should then either rotate down or come off. Then pull the light assembly to the surface and set on the deck. Then scrub the niche. Leave the light out during the SLAM.
 

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