Green Algae Will Not Die!

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N

nasparkles

0
Sep 26, 2016
43
Helena, Al
Pool Size
20000
Surface
Vinyl
Chlorine
Liquid Chlorine
I have been fighting algae all summer. At first, I thought it was mustard algae, but at some point, the yellow sandy stuff turned to green slimy spots. The spots are only on the bottom surface of the pool and are easily vacuumed out. The water has been crystal clear. I adjusted chemicals after I ordered my TF-100 test kit and realized alkalinity was too high...
PH 7.5
Alk 90
CH 240
CYA 20
Above ground, 30 foot round pool. Holds about 21000 gallons.
Started slamming process and I still see green spots after about 50 hours of having chlorine levels above 15 ppm. I vacuum to waste every morning and evening. I have zero chlorine loss overnight. CC is 0.5 and has been from the beginning. Looking at the numbers, it would appear I have no problem...except that I come out every morning and evening and see these bright green splotches of algae again! Any ideas? Also, with all of the vacuuming to waste, I am replacing a lot of water. Wondering if my loss of chlorine during the day is now more due to the level of cya in the pool. Prior to slaming, I had no problem with chlorine loss...i.e I shocked the pool at 20ppm cya and it took 3 sunny days for the chlorine to drift back down to normal levels. I'm so confused I'm crying on the inside right now. ?
 
Donldson said:
SLAM level for 20 CYA is 10 ppm FC, per the FC/CYA Levels. Where are you getting "above 15" from?
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My pool calculator listed 14 ppm FC for mustard algae, so I don't want the level to go lower than that. Keeping it above 15 gives me some wiggle room in case I burn off more chlorine than expected before I get back for the next reading.
 
Mustard algae levels are for 24 hours after the end of the regular SLAM. You are risking damaging your vinyl liner with these levels FC at your low CYA.
 
mknauss said:
Mustard algae levels are for 24 hours after the end of the regular SLAM. You are risking damaging your vinyl liner with these levels FC at your low CYA.
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Okay, thank you, that's good info that I haven't read anywhere before. So, since my overnight chlorine loss is zero, how else can I tell when the regular SLAM is "finished"? Also, if I have been at mustard levels for 50 hours, shouldn't the algae be dead by now?
 
Algae develop a protective coating, especially the ones that stick to surfaces like walls. You have to brush to remove the membrane and let the chlorine get at the algae it to kill it. Brush every day during SLAM.
 

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I would defiantly start by bumping your CYA level up as that’s the easy first step. I’d start with aiming for 40ppm as you can work up from there. The green spots are somewhat tricky but I suspect a large part is due to the FC drop during the day. I’m guessing because there’s little to nothing protecting your FC during the day you’re falling below the FC/CYA level just a touch. Let’s see what happens once we can get you holding some FC during the day.
 
Leebo said:
I would defiantly start by bumping your CYA level up as that’s the easy first step. I’d start with aiming for 40ppm as you can work up from there. The green spots are somewhat tricky but I suspect a large part is due to the FC drop during the day. I’m guessing because there’s little to nothing protecting your FC during the day you’re falling below the FC/CYA level just a touch. Let’s see what happens once we can get you holding some FC during the day.
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Okay, I will start adding CA this evening and take it from there.
 
nasparkles said:
Okay, I will start adding CA this evening and take it from there.
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Update: I added CYA while continuing the SLAM process. In total, we spent about 8 days SLAMming, with the green spots diminishing more and more as we approached day 8. I reached the point were I saw the tiniest amount of debris in the pool, but couldn't tell if it was algae or just dirt. I'm talking about one, tiny spot in a 30 foot pool. This is where I made my mistake. I became hasty and did the 24 hour mustard algae shock, and then allowed the FC to drift back down. The pool was clear for a few days, until the FC level hit 5, then the green spots slowly started reappearing. Again, I wasn't convinced it was algae, and thought maybe it was just dirt. I allowed it to stay in the pool to see what would happen, and in a matter of days, there were green spots all over the bottom again. I realize now that I should have continued SLAMming until the bottom was perfectly clear. I am going to start all over again, but I have a few questions..
1.) Do I need to consistently keep my FC level higher due to the pool being susceptible to mustard algae? I believe I read that the minimum FC should be at 14% of the CYA level?
2.) Are there any special actions that I will need to take at pool closing time in order to prevent it from being there, waiting for me when I take the cover off?
 
You likely don't have mustard algae. You have regular algae. The SLAM process is fortunately very specific...

The answers to your questions are all about maintaining FC.

Leave the covers off while SLAMming. The CC needs to offgass.
 
frogabog said:
You likely don't have mustard algae. You have regular algae. The SLAM process is fortunately very specific...

The answers to your questions are all about maintaining FC.

Leave the covers off while SLAMming. The CC needs to offgass.
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I don't have a cover, and I have never had more than 0.5 CC. Never lose chlorine overnight either. Thanks for your input.
 
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