I opened my pool the week end before Memorial day. Water was crystal clear. Added 6 lbs cyanuric acid which brought me to 40PPM. Brought the PH to 7.6PPM from 7.2PPM, total alkalinity to 100PPM from 60PPM, calcium hardness to 240PPM from 180PPM, free chlorine to 3.5PPM from 0. Checked the water for 5 days straight. Everything was fine aside of adding a little chlorine. Put the solar cover on the Friday before Memorial day. It has been on since then. 3 years ago and the 2 years prior was a nightmare with chlorine lock. Took 12 to 16 gallons of 12.5% to get rid of it. Just went out to test the water and it is completely expletative out of wack. Chlorine is non existant an hour after dumping 2 gallons of 12.5%. Normally 42oz brings it up a little less than 1PPM, PH went from 7.6 down to below 7.0. Cyanuric acid is down to 10PPM from 40PPM. 5 days ago everything was fine! The only thing that is ok is the total alkalinity 100PPM. I'm demoralized. The weather the last 4 days has been way below normal temp wise and cloudy damp. There is a lot of pollen on the solar cover. Is it possible the solar cover is causing this? How is this possible?
Chlorine lock why!!!
- Thread starter VinnyFindley
- Start date
- Jun 22, 2014
- 51,990
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Simply put - algae. You recently opened and on a couple occasions and the FC fell to zero or very close to it. Now you have a pool cocktail that seems to be a bit unpredictable. I would recommend the following:
1 - Using liquid chlorine, increase the FC to 10. Add nothing else to the water right now. Test the FC again in 10 minutes. If it fell below 5 ppm, bump it back to 10 ppm and re-test in 10 min. Continue this drill as much as needed every 10 min until the FC starts to hold between 5-10 ppm for 10 min.
2 - Once you see the FC holding, test the pH one more time. If it's 7.0 or higher, go to the next step. If the pH is definitely below 7.0, increase it slightly to get over the 7.0 hump.
3 - With the FC holding, now it's time to add stabilizer for a CYA goal of 30.
4 - Finally increase the FC to 12 and hold it there until you pass all3 SLAM criteria.
1 - Using liquid chlorine, increase the FC to 10. Add nothing else to the water right now. Test the FC again in 10 minutes. If it fell below 5 ppm, bump it back to 10 ppm and re-test in 10 min. Continue this drill as much as needed every 10 min until the FC starts to hold between 5-10 ppm for 10 min.
2 - Once you see the FC holding, test the pH one more time. If it's 7.0 or higher, go to the next step. If the pH is definitely below 7.0, increase it slightly to get over the 7.0 hump.
3 - With the FC holding, now it's time to add stabilizer for a CYA goal of 30.
4 - Finally increase the FC to 12 and hold it there until you pass all3 SLAM criteria.
- Jun 22, 2014
- 51,990
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
At this point, forget the TA or anything else, it's all about maintaining the FC of 12 until you pass the SLAM. After that, be sure to maintain the proper FC for your CYA as noted on the FC/CYA Levels. When the FC is allowed to fall below that minimum line, especially at spring opening, anything can happen. Next year I would recommend performing an Overnight Chlorine Loss Test as soon as you open. It could prevent some headaches down the road. Good luck!
Thank you! Will have to go out and get a couple of 4 gallon cases tomorrow. Only have 3 gallons on hand after dumping 2 in about an hour and a half ago. I cursed myself by saying WOW! this was just about the easiest time balancing my pool water in a long time. Last year never used the solar cover. Water was 78 by the 2nd week of June and stayed above 80 the whole summer averaging 85 from the middle of July through almost all of August. Never had a problem with the water.
- Jun 22, 2014
- 51,990
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
This has been an odd season for many across the country. But once you arm yourself with enough chlorine tomorrow, I'm sure if you follow the steps above you'll break through it. 
It's possible that the CYA was eaten by bacteria and converted into ammonia.
The dropping pH is a good indicator of that happening.
The dropping pH is a good indicator of that happening.
Make sure that you are testing for FC and CC after adding chlorine.
Looks like you caught it before it converted all of the CYA into ammonia.
A SLAM will work, but you have to maintain the chlorine at SLAM level to get the ammonia cleared as quickly as possible.
Looks like you caught it before it converted all of the CYA into ammonia.
A SLAM will work, but you have to maintain the chlorine at SLAM level to get the ammonia cleared as quickly as possible.
It's likely that you have the bacteria in your area that eats CYA, so you have to be especially vigilant about maintaining your FC at good levels.
Multiple examples of this happening happen when the pool is covered, so there might be some reason that it is more likely to happen when the pool is covered, but I don't know why it would make any difference.
Maybe it's easier to lose track of the FC when it is covered or maybe some other reason or maybe it makes no difference.
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One good diagnostic for ammonia is falling pH while adding chlorine because oxidizing ammonia is acidic.
2NH4+ + 3OCl- --> N2 + 3H2O + 2H+ +3Cl-
When adding 12.5% sodium hypochlorite (liquid chlorine) to a pool to oxidize ammonia, every gallon of liquid chlorine will create the equivalent of 15 ounces of 31.45% hydrochloric acid.
2NH4+ + 3OCl- --> N2 + 3H2O + 2H+ +3Cl-
When adding 12.5% sodium hypochlorite (liquid chlorine) to a pool to oxidize ammonia, every gallon of liquid chlorine will create the equivalent of 15 ounces of 31.45% hydrochloric acid.
Thank you Texas and James! Wow very informative. My pool is going to take a back seat until the week end. Working unexpected over time and my father in law was hospitalized. I have Fridays off so I will start the slam Thursday night and will be able to maintain through the week end. Just kills me that everything was perfect and went to poo rapidly. Starting from scratch when all was well. Last time this happened it took 14 gallons of 12.5% to solve the problem. 1 case of 4 gallons before I was getting any reading.
- Jun 22, 2014
- 51,990
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Take care of family. The pool will be there when you get back. So will we. 
Another good way to tell if it is ammonia is if the chlorine is consumed rapidly but there is no sign of any algae color like green or yellow.
Ammonia is clear and colorless.
The water will usually look dull and cloudy.
You can have algae and ammonia, which makes it harder to deal with, but a SLAM will get you back to good soon enough.
Ammonia is clear and colorless.
The water will usually look dull and cloudy.
You can have algae and ammonia, which makes it harder to deal with, but a SLAM will get you back to good soon enough.
This is exactly what I'm dealing with. No algae green or yellow but dull and cloudy water! You can see the bottom in the shallow end of the pool. Barely in the deep end where the drain is. Massive amount of pollen on the solar cover. That's coming off when I do the slam. No trees in my yard but my yard borders a large wooded area and my neighbor where the wind comes from mostly has a lot of trees that drop debris when they bud in spring time that get into the water!
Just be aware that the amount of chlorine needed goes up a lot every day that you delay.
I'm aware. If I start a slam and I'm not here during the day to keep up with it, I'd be wasting that way also. Out of the house at 5:00 AM and get home around the same time PM. Don't trust anyone to help me with the slam process!
Dumped 3 gallons of 12.5% in a few hours ago. Measured a faint pink reading. Didn't complete the test just dumped 2 more gallons in and will test again in about an hour. I think the massive amount of pollen was the culprit. Pulled the solar cover off and almost threw up rinsing it off. Total gross out. 0 science in that thought just an educated guess!!!
- Jun 24, 2021
- 15,605
- Pool Size
- 29000
- Surface
- Vinyl
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-60 Plus
How does the ammonia get in there when the water was crystal clear and all chemical levels were good? Is it not possible that the massive amount of pollen caused it? Just asking. The pollen after rain does leach into the pool from the solar cover!