Fixing Ammonia Pool Problems
What Causes Ammonia in Pool Water?
When closing a pool over the winter and letting it go by not adding chlorine to it regularly or not having sufficient algaecide, then soil bacteria that gets into the pool can grow and convert Cyanuric Acid (CYA) into ammonia.
For every 10 ppm CYA that is decomposed, it produces around 3.3 ppm ammonia (measured as ppm Nitrogen) and would require around 30 or so ppm FC to get rid of it. Fortunately, ammonia is a little volatile so some of it may outgas.
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 an ammonia test kit at a pet store.
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?
to be written
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 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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