Re: Humic Acids in Nature vs the Aquarium (Long)
As some of you may recall, last month I was on a tear to find out what
level of Tannins and Humic Acids existed in tropical blackwater biotopes.
Some companies (and authors) seem to think that a certain level of these
substances are beneficial (why else would so many companies be peddling
"Blackwater Extracts"?) while others caution that these substances can be
harmful if present in excess.
My query was an attempt to determine what the natural levels of these types
of substances were. The fish have evolved over thousands of years in these
types of waters and I felt that if we had an idea of the concentrations in
Nature we would be in a better position to deal with them in an aquarium.
Several people on the list came forward with information, my thanks to
those who did. I also contacted several companies which produce "Blackwater
Extracts". Unfortunately, none of them bothered to even acknowledge my
query (Shame on you, Tetra/Second Nature!!!)
I finally went to Dupla. Kaspar Horst of Dupla was kind enough to forward
my query to Prof Dr Rolf Geisler, who provided me with a detailed answer.
What follows is the translated text of that response, as prepared for me by
Dupla. Mr. Horst has givn his premission for this material to be placed on
A special answer for Mr. James Purchase, Toronto:
Concentration of humic acids and tanning agents in tropical black waters
Humates in their full sense - and not just humic acids - are an important
buffer systems for typical black waters with extremely low lime contents. A
precise analytical registration of the chemical complexe humates, dark
organic colloids, is very complicated and requires considerable technical
equipment that is only available in a few special laboratories.
It is much easier to measure the content of "organic substances" and thus
also the humates contained in the water. All organic substances are carbon
linkages. In this way it is possible to determine the DOC (Dissolved
Carbon) or the TOC (Total Organic Carbon). This however requires the use of
gas chromatograph - a very expensive device - and a lot of technical
Since the beginning of tropic limnologic research a relatively simple
measurement method has been used: the determination of the co-called
potassium permanganate consumption (KMNO4-consumption in mg/l). In this
measurement the organic substances are destroyed by means of the oxydizing
agent potassium permanganat, thus becoming measurable. The determination is
carried out by cooking a given quantity of water with a permanganate
of exactly known content for about 10 minutes. For this method one needs a
certain laboratory equipment with chemicals, glass devices and cooking
facility - short: it is quite expensive !
Despite the well-known objections to this not really optimum determination
humates with the permanganate method, also recent tests of tropical fish
waters have been carried out in this way, so to allow comparison with
of former examinations. Unfortunately, there are no conversion factors for
permangante consumption to DOC or vice versa.
Back to the initial question: Information about the permangante consumption
(sometimes indicated as "oxydisability") in biotops of tropical aquarium
and typical black waters is available. Here some figures:
KMnO4-consumption in mg/l
up to 12 low, gun-laying data for dringking-water
20 to 56 biotope of Red Neon
26 to 59 biotope of Discus Heckel
13 to 27 biotope of "Brown Discus"
> 100, up to 250 max. biotope of labyrinth fish is eas- and west (asia)
Now to the most important question: How is it possible to reach a certain
level of humates in the aquarium?
There are various methods of supplying humates to an aquarium. Known is the
filtering over unfertilized peat, peat extracts, peat pallets, leaves,
oak-tree bark extracts and other preparations containing tanning agents.
These are many possibilities - but one important questions is still
unanswered. How much of the above mentioned substances is needed to reach
values as found in nature. It would be nice to have indications like,
so-and-so much peat granules or so-and-so many ml peat extract on a certain
quantity of water of clearly defined composition produce organic substances
corresponding to so-and-so many mg/l permanganate consumption. Why doesn't
this sort of information exist ?
First, the available sources of humates are not standardized, e.g. peat as
substance differs considerably depending on it's origin and storage place.
Indications such as " ... contains so-and-so many g peat extract" do not
really say anything about the quantity, since the concentration of the
extract is unknown or not indicated - admittedly also difficult to say!
important to know: The harder the water the more ineffective the humic
- more exactly: the dissolved lime in the water produces undissolvable
calcium humates. So, the higher the water hardness, the higher must be the
supply of humates in order to achieve an acidifying effect. The softer the
water, the less humates are needed and the better the effect.
Conclusion: As the values of water hardness are worldwide different and the
concentration of humates are not standardized, to make a simple calculation
and state"In order to achieve a Neon water with 25 mg/l permanganate
consumption or a black water for chocolate-guramis with 80 mg/l, procede as
follows ..." Therefore the only things that will help an aquarist are his
experience and a water that is not too hard.
Further literature may be asked for at our editorial department.
jpp at inforamp_net