Fixing Ammonia Pool Problems
If you have ammonia you ABSOLUTELY SHOULD NOT ADD anymore CYA!
What Causes Ammonia in Pool Water?
The most common situation is when a pool is closed over the winter without adding chlorine to it regularly or not having sufficient algaecide. That allows soil bacteria that gets into the pool to grow and convert Cyanuric Acid (CYA) into ammonia.
For every 10 ppm CYA that is decomposed, the bacteria produces around 3.3 ppm of ammonia (measured as ppm Nitrogen) and would require around 30 or so ppm FC to get rid of it.
What are the Signs that Ammonia is in Pool Water?
- Disappearing CYA
- High CC
- Low ph
- Inability to hold chlorine level
How do You Test Pool Water for Ammonia
Get a simple ammonia test kit at a pet store from the aquarium section, they’re about $8.
Caution using a aquarium ammonia test. Aquarium testers are not designed to handle chlorinated water. The high oxidizer levels will almost surely screw up the test. The presence of chloramines may also interfere with the ammonia test.
If chlorine is measurable at any concentration, ammonia can not exist and vice versa. The two react very rapidly with one another turning into chloramines.[1]
What is the Treatment for Ammonia in Pool Water?
Confirm that You Have an Ammonia Problem in Your Pool Water
- Your CYA will be 0
- Add chlorine for 10 ppm and test your free chlorine after 30-minutes. You likely have ammonia in your water if you lost 80%+ of FC in 30 minutes
- Your CC tests > 0.5
- Optional: An ammonia test indicates the presence of ammonia
Getting Rid of Ammonia in Pool Water
- Dose the pool to SLAM level of 10 ppm
- Do not add any CYA until chlorine begins to hold
- Test chlorine every 30 minutes until chlorine begins to hold. Add chlorine as needed to get back to 10 ppm. FC will likely test close to 0 until you get to the next step
- You will know when the chlorine begins to hold when you begin seeing FC testing > 3 ppm after 30 minutes.
- When you see a significant jump in FC from the prior 30 minute test CYA can be added back into the pool. Limit the CYA to 30 ppm for the duration of the process
- Increase the FC target to 12 ppm and follow the steps in the SLAM Process until the criteria of “Done” are all met.
- Follow the SLAM Process FC test procedures. You no longer a need to test every 30 minutes at this stage.
To recap, the distinguishing characteristic for ammonia in the pool is when chlorine gets consumed VERY quickly to go to an FC of zero -- within a minute or so. The prescription is to keep adding chlorine until the FC starts to hold, at least slowing down significantly in its consumption rate. If one can test and add chlorine every 30 minutes, that would be fine to do during the early stage. Once the FC is holding and more slowly dropping, one can test and add over hours (2-4) and extend the time according to the rate of chlorine loss. The key is to rapidly get to a point where there is FC and then keep adding chlorine to maintain an FC or at least not let it get to zero.
Tips When You Have Ammonia in Pool Water
- It takes about 10X the amount ammonia in FC to convert an ammonia pool. So if, for example, your pool has 20ppm ammonia, it will take 200ppm FC to convert it all.[2]
- Ammonia can happen mid-season if a pool is at zero FC for too long
- 0 ppm CYA alone doesn't mean there is an ammonia problem
- CYA need not be 0. It's possible for the bacteria to stop for whatever reason so the requirement is that there is a DROP in CYA that is unexplained, not that it goes all the way to zero. Note also that an unexplained drop in CYA does NOT mean there will be ammonia, only that there MIGHT be ammonia. Different bacteria can continue to oxidize the ammonia to nitrogen gas in which case (if you're lucky) you will not have any extra chlorine demand.
- If pool water has 0 FC and 0 CYA you may want to do a 10 ppm chlorine test for 30 minutes and see the water holds chlorine before adding CYA.
- When the bacteria causing ammonia is in the water adding CYA will just create more ammonia
- Nothing consumes chlorine as much and as fast as ammonia
- Bacteria will get killed as chlorine is added
- Ammonia can come from some algaecides
What is the Chemistry behind CYA being Converted to Ammonia in Pool Water?
Soil bacteria that gets into the pool grows and converts Cyanuric Acid (CYA) into ammonia. The net equation is as follows:[3]
C3H3N3O3 + 4H2O --> H+ + HCO3- + 3NH3 + 2CO2 Cyanuric Acid + Water --> Hydrogen Ion + Bicarbonate Ion + Ammonia + Carbon Dioxide
What is the Chemistry when Ammonia is cleared from Pool Water?
When you first add chlorine, it converts the ammonia to monochloramine which registers as Combined Chlorine (CC) and this happens in seconds with no CYA or about 1 minute with 30 ppm CYA.
HOCl + NH3 --> NH2Cl + H2O Hypochlorous Acid + Ammonia --> Monochloramine + Water
Then, additional chlorine oxidizes the monochloramine to the products shown below and with no CYA in the water that takes around 10 minutes for 90% completion. With 30 ppm CYA, it can take several hours.
So generally speaking it is best to not add more CYA until one gets rid of the ammonia.
There will be more nitrogen trichloride produced, but that is easily removed through outgassing and breakdown from sunlight:
HOCl + 2NH2Cl --> N2(g) + 3H+ + 3Cl-+ H2O Hypochlorous Acid + Monochloramine --> Nitrogen Gas + Hydrogen Ion + Chloride Ion + Water
Note that the above reaction is acidic, but it exactly compensates for the alkalinity (high pH) of hypochlorite sources of chlorine. It takes three hypochlorous acid to oxidize two ammonia.
On a ppm basis, this is a chlorine to ammonia ratio of 7.6, but greater efficiency to completion is achieved using a ratio of 8-10 so that is where the 10x rule comes from and it only applies to ammonia measured as ppm Nitrogen, NOT to monochloramine.
You can see that it takes one hypochlorous acid to oxidize two monochloramine so that's a little more (for efficiency) then an FC level of half the CC level.
The net reaction of oxidizing ammonia using a hypochlorite source of chlorine may be written as:
3OCl- + 2NH3 --> N2(g) + 3Cl-+ 3H2O Hypochlorite Ion + Ammonia --> Nitrogen Gas + Chloride Ion + Water
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