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==Ammonia in Pool Water== | ==Ammonia in Pool Water== | ||
| + | ==Signs of CYA conversion to Ammonia== | ||
| + | *disappearing CYA | ||
| + | *high CC | ||
| + | *low ph | ||
| + | |||
| + | ==How Ammonia Forms== | ||
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'''''.<ref>https://www.troublefreepool.com/threads/opening-a-pool-to-high-chlorine-demand-ammonia.6398/</ref> | 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'''''.<ref>https://www.troublefreepool.com/threads/opening-a-pool-to-high-chlorine-demand-ammonia.6398/</ref> | ||
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'''''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. | '''''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. | ||
| + | ==Treating Ammonia== | ||
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. | 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. | ||
Revision as of 04:22, 19 August 2019
Ammonia in Pool Water
Signs of CYA conversion to Ammonia
- disappearing CYA
- high CC
- low ph
How Ammonia Forms
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.[1]
The net equation is as follows:
C3H3N3O3 + 4H2O --> H+ + HCO3- + 3NH3 + 2CO2 Cyanuric Acid + Water --> Hydrogen Ion + Bicarbonate Ion + Ammonia + Carbon Dioxide
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.
Treating Ammonia
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
