Toxicity of Ammonia in acidic and basic water - The Planted Tank Forum
 
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post #1 of 3 (permalink) Old 01-04-2017, 02:50 PM Thread Starter
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I read a book by Walstad regarding the experiment comparing ammonium ion and nitrate. According to the result most aquatic plants utilised ammonium more readily than nitrate. The only question regarding the experiment is that she use 2ppm instead of higher level of ammonium.
I believe when ammonia dissolve in water it readily accept proton to form Ammonium hydroxide, which is basic. After that the ammonium hydroxide may react with acidic compound to form ammonium salts which also soluble in water. In other words, in lower pH more dissolved ammonia form ammonium in water which are relatively harmless.
NH3 + H2O -> NH4+ + OH-
In CO2 enrich water
2NH3+H2O+CO2 -> (NH4)2CO3
Since we normally dose around 20-30ppm of co2 most ammonia will react with carbonic acid to form ammonium ion.
However when water pH is high ammonium ammonia equilibrium will shift more to the left. In other words more ammonia will be present in water instead of ammonium.

sometimes I suspect plants may not dead due to high ammonia level,in acidic water it may be in the other way round. Plants death cause increase in ammonia. High pH water increase toxicity of ammonia in water to fish. However it still remain undecided whether ammonia molecule in stead of ion are toxic to aquatic plants. I'm still wandering is there any scientific journal covering this topic.

p.s. all my idea are base on logic speculation and may not work the same way in real life. Any one who work in scientific field should devise an experiment and let us know the result.


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Another information. This is the chart used in aquaculture for measuring the ratio of ammonium and harmful ammonia after measuring total ammonia level with test kit. Example, at 25 degree Celsius, when pH is 6 0.06 percent of ammonia will be in molecule NH3 form. When pH raise to 8 (as in hard water etc) , 5.38 percent of total ammonia will be in molecule NH3 form, a total increase of 89.67 times.

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Last edited by Darkblade48; 01-04-2017 at 11:02 PM. Reason: Please use the edit function for back to back posts to keep threads cleaner
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post #2 of 3 (permalink) Old 01-04-2017, 08:32 PM
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Cool chart
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post #3 of 3 (permalink) Old 01-04-2017, 09:04 PM
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Quote:
Originally Posted by John Wong View Post


Another information. This is the chart used in aquaculture for measuring the ratio of ammonium and harmful ammonia after measuring total ammonia level with test kit. Example, at 25 degree Celsius, when pH is 6 0.06 percent of ammonia will be in molecule NH3 form. When pH raise to 8 (as in hard water etc) , 5.38 percent of total ammonia will be in molecule NH3 form, a total increase of 89.67 times.

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Reposting this here as its more appropriate.

I have always understood ammonia is more toxic at a higher PH. But now I'm starting to understand the why. So in essence a test kit that tests combined NH3 and NH4 is not a good indication of ammonia. My Nutrafin test kit says NH3 which makes me happy because this is the only value that we need to worry about providing we have a stable ph. Which also tells me that ammonia should never be tested during Co2 injection and probably best tested right before the Co2 kicks in.

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