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[APD] Ammonia

I believe David Marshburn wrote this email section below:

Stuart Halliday wrote:
So in theory by adding ammonia drops to my tank, the plants would only take up the ammonium part and leave the free ammonia behind?

sort of. free ammonia and ammonium are in some equilibrium, depending on pH. as plants pull out the ammonium, some of the free ammonia will shift to ammonium ion (and i suspect that the pH will be affected).

I thought that.

here's the first article on ammonia/ammonium equilibrium that popped up on google, and it seems pretty good, if maybe a bit mathy.

Oh lovely link. Thanks.

notice that, in order to go from ammonia to ammonium, the ammonia had to snag an H+ from the water, leaving a free OH- hanging around (this is why ammonia solution is considered basic).

So the ph will rise and move towards the alkaline, buffering permitting?

also, the relative fraction of ammonia and ammonium is affected by pH. at pH of 9.24, it's a 50/50 split. at higher pH, there will be more ammonia; for "most" (?) planted tanks, the pH is closer to neutral, so most of the ammonia is in the form of ammonium.

Yes, I've noticed that.
A friend of mine was sweating buckets over a new tank with a pH of 7.4 @ 25C and a TA of 0.25. I said don't worry too much about it. That's 0.004ppm of NH3. Virtually harmless to his adult fish. I said, just use Prime or do a 25% WC if he was worried and eventually it will go away. It did.

this calculator will tell you how much ammonia vs. ammonium you have, based on total nitrogen concentration, pH and temperature

Ah good old Professor Alleman.
We can find his original equations here:
or via my Ammonia page.

I quite like this online chart below as it shows the toxicity levels:

A few months ago, I managed to find where these 'toxicity levels' came from
if anyone is interested:

US Environmental Protection Agency. Ambient Water Quality Criteria for Ammonia, (EPA 440/5-85-001). January 1984-2004


Stuart Halliday
200 Million years in the making...
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