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Hi Guys,

It has been a while since I have used any of this stuff.

I bought a nitrate test kit that states readings over 110 mg/L need a water change. I would have thought it is much lower than this.

Is this a different reading than the normal PPM reading?

For all intents and purposes, mg/L equals ppm for dilute aqueous solutions.

Joe Potato

Hi,
The accepted practice and train of thought seems to be
that with well planted tanks, one should strive to keep
the nitrate reading between 10 and 20. In a fish only
tank, as near 0 as possible not to exceed 40.
Tanks with nitrate readings of 40 and over are in serious
need of cleaning. The main source for that reading is in
the gravel and it should be cleaned with each water change.

THE main source of the nitrifying bacteria is in the gravel
and then the filter.

When cleaning the tank one should mentally divide the
non planted portions of the tank into 3 or 4 sections
and with each water change, clean one section. With the
next water change clean the next section, etc. That way
if doing weekly water changes, in a month you have cleaned
the entire tank. Moving from one section to the next with
each change leaves the newly cleaned section to recover,
while rest of the tank sustains the cycle.

Tanks with nitrate readings of 100+ indicate the beginnings
of OTS or Old Tank Syndrome and described here:

http://www.bestfish.com/oldtank.html

In short, do regular water changes, feed sparingly, stock
lightly, clean the gravel a little at a time, and you will
keep your nitrate readings low.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

Frank, I have some comments about the link you provided:

At a pH of about 5.5 or less, the bacteria that usually convert ammonia to nitrite are inhibited, so ammonia levels begin to rise. Strangely, though, the low pH actually protects the remaining fish by keeping the ammonia in the non-toxic ammonia (molecular) form instead of the very toxic ammonium (ionic) form!

It seems to me that with a low pH, the protonated NH4 should be the most common form as there would be an excess of H+ ions. Additionally, I would think that normal NH3 would be the most harmful form as the ionic NH4 would have trouble penetrating cell membranes. Is my thinking wrong?

Joe Potato

Hi Joe,
To tell you the truth it has been over 20 years since I've
had to apply any "real" chemistry and frankly, I don't
know the answer to your specific question.
My last chemistry class was GEO CHEM a 500/600 level course
and it, and I, were more interested in the effects of
massive pressures and temperatures on magma than the
reactions of ammonia and pH.

However, in searching the internet, I have found the
following:

http://www.bluemoon.net/~tammy/profiles/water.html

Additionally, in the ECOLOGY OF THE PLANTED AQUARIUM, 2nd
edition, by Diana Walstad, on page 20, she addresses
the subject, Ammonia.
Quote:
NH3 + H2O <> NH4OH <> NH4+ + OH-

The percentage of ammonia in a solution with a given N
concentration changes dramatically with pH. Typically,
there is a 10 fold increase in ammonia for every 1 unit
increase in pH as NH4+ converts to NH3 in the above
equilibrium reaction. For example, if the pH increases
from 7.0 to 8.0, the % of the N that is NH3 increases
from about 0.33% to 3.3%, while the % of N that is NH4+
correspondingly falls from 99.7% to 96.7. Thus the higher
the pH the greater the NH3 concentration and the toxicity
of a given concentration of inorganic nitrogen.
Endquote
Her reference for this information is from Professor
Robert Wetzel, Professor of Limnology, and a text titled
LIMNOLOGY, 2nd ed, Saunders College Publishing.

There are other sites that have similar comments about
the toxicity of ammonia and how it decreases as the pH
decreases, but I don't find any specific references for
that information, just general statements. They may just
be paraphrasing others work, or simply passing on comments.
You may want to research other papers in the field
of Limnology for the "chemical" derivations/equations
to support your thoughts.

Frank

-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

Thanks for the reply, Frank. I find it interesting, though, that the link and the excerpt from the book contradicts the link in your first response, as the information in the sources in your second response indicates that NH4+ is the less toxic form and is the most abundant in lower pHs. To put the matter to rest, I'll go through the research database and ask our resident ichthyologist at my college when I head back to school in about a week. We'll see what the experts say.

Joe Potato