http://www.epa.gov/waterscience/crit...references.pdf

Read all these and you will be an expert.

Regards,
tom Barr

I have decided not to become an expert on ammonia. Tough decision, but after a couple seconds of perusing that list I managed to make it.

Even Scots seem to be kidding from time to time.......

Very busy reading
Detlef

Looks like most of those articles are about the toxicity of ammonia to various animal species, correct?

Yes, it's an exhaustive listing for a wide range of critters, many are inverts, which tend to be more sensitive.

Such studies are the basic criteria for setting toxicity and appropriate levels for various systems and acceptable limits.

When we approach what is an "acceptable limit", this is where some folk's brains turn to mush. While it might be nice to have the purist nicest water in the world, the reality is that it's just not going to happen, we do not have enough $, time or labor to do it, same applies for the EPA as it does for us.

So what is a reasonable level?
NH4?

I'm not sure.

But I do know that it can induce many issues, cause algae, kill fish etc.
and at very low levels, levels I have trouble measuring without advanced methods.

NO3?
It's very high before it becomes a problem.
Same for K+, and PO4.

How about CO2?
Where does it become a problem and why?

Some references suggest a real issue at 10-20ppm.
Some suggest it's not an issue at pH of 6-8 until we get to nearly 100ppm.

Our own use suggest about 30ppm and plants do not really gain beyond that amount anyway.

But what is used for a control?
That's a key question for aquarists using their tanks to imply research, test or a "study".

Such controls are sorely lacking.

You need to have healthy fish, healthy plants, nice healthy stable tank and be able to do this with ease.

You need to be certain that there are no inducible limitations, or limitations to start with. Even scientific research gets their research methods wrong.

A classic example is with respect to alleopathy and most of the citations and synthesis Walstad did. Her assumptions where based on that research, however, the research suggested that extracts ground up where the same as endogenous chemicals. Plants have all sorts of chemicals inside them, does not mean they ever release them and target another species.
Maybe it's a secondary effect..........the plant root gives off something that the bacteria use and the bacteria produce a allelopathic chemical that kills/inhibits another plant.

Still, what would you use as a control here?
Activated carbon would be good, but it can remove some other things as well such as plant nutrients. So a good non limiting nutrient level would need to be in place for both systems.

I've never seen it in an aquarium either between plant= plant interactions, this is where such chemical warfare would be most visible and prevalent, not killing algae.

NH4 is a good place to start, it's a good indicator that bacteria, plants, and algae are not present and actively growing/using this ion.
A subtle change in NH4 could tell rapidly if there's something else present.

The control here is not adding any source of NH4, while adding it to another system.

You can see the toxicity, the algae, and the growth.
Allelopathy, NO3, PO4, K+ etc...........no until you get very high levels.


Regards,
Tom Barr