when does ammonia become toxic to plants - The Planted Tank Forum
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post #1 of 7 (permalink) Old 09-27-2007, 11:24 PM Thread Starter
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when does ammonia become toxic to plants

at what ppm does ammonia become toxic to plants? Just curious.
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post #2 of 7 (permalink) Old 09-28-2007, 01:01 AM
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over 2 ppm i'm thinking. I remembered somebody having 4ppm of NH4 and their plants were melting.

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post #3 of 7 (permalink) Old 09-28-2007, 06:16 PM
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Directly from this and in direct contradiction with Diana Walstad's claim in her book:

"While one might expect NH4+ to be preferred by plants, as its assimilation requires less energy than that of NO3-, only a few species perform well when NH4+ is the only, or predominant, source of N. By contrast, most species develop toxicity symptoms when grown on moderate to high levels of NH4+ (1-6), whereas normal growth in these species is seen on NO3-."

When applying a routine to supply nutrients, it's likely best to suggest that mostly NO3 and a little NH4 from fish waste, perhaps decaying plant parts etc is the best solution.

There seems to be a temptation to assume there is "a preference" and it can be applied to all plants. There is no support for that speculation. the other issue left out oif the disccusion that you bring up is how much are we talking about?

0.1ppm? 0.5ppm? 1, 2, 5ppm?
What's safe for the other critters like fish and shrimp?
What about bottom fish that right next to the soils?

Further, if you consider the NH4 issue as far as rate of uptake specifically in aquatic plants, at less than 0.5ppm of NH4, NO3 uptake rate is faster in Elodea. If you use rate of uptake to suggest plant preference, then the answer is no, NO3 is preferred at less than 0.5ppm of NH4.
But preference is not merely defined to a few hours of uptake studies, you would also need to consider growth totals with various NH4 and NO3 ratios.
Grow things out for several weeks and take the relative growth rates from the dry weights.

So unless you plan on having rather high levels of very toxic NH4+(to fish let alone plants), this notion has some serious flaws in support.

The references for support should match the conclusion
That was not done.

So in answer to your question, yes, for many species, high levels will kill the plant, but other factors such as temp and pH play a role, as well as other ions present in the water to balance the internal ion charge and ability of the plants to balance those charges.

So it depends a lot on many things how much is required to kill plants, but high levels will certainly "harm" them(less growth, more respiration etc). Rice and some other plants can handle, or tolerate high levels, but it does not "help" them.

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post #4 of 7 (permalink) Old 09-28-2007, 06:40 PM Thread Starter
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Good to know!

I have a tank that I'm currently in the midst of a fishless filter cycle using NH3 that is at about 4 ppm. I was considering storing some plants in that tank but instead elected to set up a 10 gallon for some short term storage.
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post #5 of 7 (permalink) Old 09-28-2007, 10:26 PM
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FYI, never use your tank to do some fool's method
Use a small bucket to cycle your filter, cheaper, easier and no testing needed.
Just start it up, add NH4, and a little dirt from outside, wait 3 weeks. That's it.

In planted tanks, FC is really not worth the effort to type even.
Plants use NH4 directly, come pre loaded with bacteria on roots/leaves etc, do not consume large amounts of O2(unless rotting).

There is no cycle in planted tanks because there are plants.
That's why they run healthier for fish and have little issue with NH4.

I suppose for fish only tanks for folks who do not live near anyone and have only one tank, FC may have some use, still, do the cycling in a bucket, never the tank.

Why add lots of NO2/NO3 which the NH4 will convert to and have to do a large water change?

In the bucket, you just dump afterwards, the tank is left alone.

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post #6 of 7 (permalink) Old 09-28-2007, 10:29 PM
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That's a great idea which had never crossed my mind before, I'll have to remember that one.

On the topic, why do you have such high levels of ammonia? You only need a small amount to start cycling. Having such a high level will only, as Tom said, end up in all kinds of nitrates in your tank that you'll end up having to change out. More ammonia does not equal faster cycling.
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post #7 of 7 (permalink) Old 09-29-2007, 03:42 AM Thread Starter
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Tom, thats a great idea. Buckets would be way cool. I just bought (a month ago) 4 tanks. One will be a quarantine tank, one a potential breeder and the other my show tank. I'm still researching, learning, etc. so I decided to start cycling filters in one of the two 40 gallons just so my wife would leave me alone about having 4 tanks with no water The bucket would be much easier and space saving.

Carissa, the NH3 is so high because I'm a newb and the article or two I read said 4 ppm was where it was at I can do a WC and bring it down though.
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