This is the first year I will be closing the pool (moved in November). Last year the previous owners closed in August. Upon opening, I had to use 40-50 jugs of bleach to get the pool to hold FC. I was told on TFP that this may be ammonia that was converted from the CYA, which I suspect is the case. Is there was way for me to prevent this from happening this year? I will be closing much later, when water temps are below 60, SLAM and add Polyquat as outlined in the 'closing a pool' thread. I also plan to open when water temps are around 60. Will this be enough, or is there some other precaution I need to take?
How to Prevent CYA to Ammonia
- Thread starter 440dodge440
- Start date
I think its more uncommon for it happen than common. I don't think there is any way to insure it doesn't happen?
You have the right idea about closing and opening around 60 degrees as any algae present will be slowed by the cooler temps.
You have the right idea about closing and opening around 60 degrees as any algae present will be slowed by the cooler temps.
- Jun 22, 2014
- 47,797
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
I suspect that by following the TFP closing procedures, you won't have any problems. The combination of your increased (SLAM) FC coupled with the colder water (60 degrees or less) do well to preserve FC for a long time and prevent CYA degradation.
- May 23, 2015
- 24,408
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
The CYA-to-NH3 conversion is caused by bacteria. One type of bacteria takes CYA and converts it to ammonia and then a second type of bacteria converts the ammonia to nitrates. Unfortunately it seems that the first process (CYA to ammonia) is much more likely to happen than the second process. Depends on the bacteria present.
That being said, it sounds like you plan to follow the TFP procedure of waiting for the water temperature to go below 60F before closing, that is good. I'm not sure why the previous pool owner you mentioned closed so early in the season (late August) but I suspect it was out of convenience for him. It's a lot easier to close a pool when you can cover it before the leaves start dropping. However, closing it when the water can remain so warm is a recipe for creating an algae farm...
So, I think you'll be good. You'll probably have to spend a good deal of time cleaning out leaves and keeping the pool sanitized while it is not swimmable (water < 78F), but by waiting and performing the closing procedure as outlined in Pool School, you'll likely save yourself from the ammonia bomb that happened in the spring.
That being said, it sounds like you plan to follow the TFP procedure of waiting for the water temperature to go below 60F before closing, that is good. I'm not sure why the previous pool owner you mentioned closed so early in the season (late August) but I suspect it was out of convenience for him. It's a lot easier to close a pool when you can cover it before the leaves start dropping. However, closing it when the water can remain so warm is a recipe for creating an algae farm...
So, I think you'll be good. You'll probably have to spend a good deal of time cleaning out leaves and keeping the pool sanitized while it is not swimmable (water < 78F), but by waiting and performing the closing procedure as outlined in Pool School, you'll likely save yourself from the ammonia bomb that happened in the spring.
You can lessen the chance for this to occur by preventing bacterial growth. Elevated chlorine levels and closing the pool when the water is cold (50ºF or colder, if possible) and then covering the pool with an opaque cover will help, but the chlorine may not last depending on water temperature and how long the pool is closed. You can use Polyquat 60 as described in this post and that should act as insurance if the chlorine level gets to zero. While it will inhibit algae growth, it might slow down bacterial growth enough to prevent a problem. You should then open the pool before the water gets too warm (i.e. before 50ºF if possible).
Thanks...the previous owner closed early because they moved before they sold the house, so nobody was around to take care of anything. I have a loop loc cover, so sunlight will make it's way in; I guess I'll take the solar cover off at night and put it on in the morning in an effort to let the water cool down to the 50 deg range (and protect chlorine during the day) once the swim season ends...
why not just check and add chlorine weekly/monthly until it freezes and then start again when it thaws
Yes, you can do that as well, but when people close a pool in freezing climates they shut off their pump (and have water below the skimmer anyway) so have no circulation. So if you want to add chlorine regularly, you need some way to mix up the cold water. One could put in a portable submersible pump to do that and move it around the pool or one could try brushing the pool, but for a larger body of water it's hard to get it all circulated well.
Diffusion is VERY slow so cannot be counted on to spread the chlorine in any reasonable amount of time. As noted in this paper, the diffusion coefficient of hypochlorous acid and hypochlorite ion at freezing temperatures is roughly 6x10-6 cm2/sec while at hot spa temperatures (104ºF) it is roughly 1.7x10-5 cm2/sec. Even using the hot spa temperature, it would take 18 hours for the concentration to get to half of what it is 1 cm away (i.e. having one volume at one concentration and another at zero concentration at 1 cm away it becomes half the concentration in 18 hours at 104ºF or 51 hours at 32ºF). You simply cannot count on diffusion to mix chemicals. In practice, thermal gradients and other factors overwhelm diffusion, but it really takes physical circulation to mix the water.
Diffusion is VERY slow so cannot be counted on to spread the chlorine in any reasonable amount of time. As noted in this paper, the diffusion coefficient of hypochlorous acid and hypochlorite ion at freezing temperatures is roughly 6x10-6 cm2/sec while at hot spa temperatures (104ºF) it is roughly 1.7x10-5 cm2/sec. Even using the hot spa temperature, it would take 18 hours for the concentration to get to half of what it is 1 cm away (i.e. having one volume at one concentration and another at zero concentration at 1 cm away it becomes half the concentration in 18 hours at 104ºF or 51 hours at 32ºF). You simply cannot count on diffusion to mix chemicals. In practice, thermal gradients and other factors overwhelm diffusion, but it really takes physical circulation to mix the water.