Re: Humic Acids

CB-- > >
James  >

> > If you all pick up a copy of AFQ from a couple of issues ago, you will 
> > find what I wrote about humic acids in marine/reef systems,

Sorry for the typo, that was "issue" and the name of the magazine is 
Aquarium Frontiers.  It used to be quarterly, hence the Q.
> > Colorimetric tests for humic acids come in two flavors.  Those that 
> > measure the amount of yellow color in the water, and those that measure 
> > the amount of reactive phenol functional groups in the water.  Hach and 
> > LaMotte sell test kits in both flavors.
> Really? I have the the LaMotte list in front of me and they show the
> Tannin/Lignin Test Kit which measures Tannin or Lignin like substances
> within a range of from 1 - 10 ppm. 

That would be the one that reacts with phenolic groups.

> Is the colorimetric test you refer to
> Lamotte's Color Test Kit which reads in ALPHA Standard Color Units? 

APHA color units, yes.  That is the water color test kit.

> Is this similar to what dupla sells? 

I have no idea.  I don't think that Dupla is exactly a powerhouse in 
analytical aquatic chemistry, so I'm not likely to go too far out of my 
way to find out, either.

> I can understand that Tannins will color the
> water, but how would various colors relate to actual ppm concentrations of
> Tannins? 

The reactivity of various tannins with the reagent is different.  So they 
may Tell you that it reads in mg/L tannic and humic acids, and at that 
point, you have to ask "which one?"

> And how could anyone be sure that the only substances adding color
> to the water were Tannins? I see that HACH also sells a Color Test Kit.
> Same deal.  

So, what else would it be?  This is yellow color.  Humic acids are 
yellow.  No one is putting yellow food coloring in your tank, so unless 
you come up with another candidate class of compounds present in high 
enough concentration to impart yellow color to the water, I'll go with 
the assumption that the yellow color is from humic acids.  

> > I would imagine that the "measure yellow color" approach might be more 
> > practical for freshwater systems, as it is for reefs.  Both the LaMotte 
> > and Hach test kits are described in my column.  The LaMotte kit is about 
> > 2x as precise and 2x as sensitive as the Hach kit.
> I would really like to find out where that article appeared. As for
> practicality, I tend to be more analytical than practical, as if people on
> the Plant List haven't noticed.

Fine with me.  The problem is that you don't know the reactivity of the 
humic acids in your tank matches the reactivity of the standard humic 
acid that Lamotte uses, so at best, you are back in the land of empirical 
correlations.  I think before you get "analytical," especially with me, 
you really need to understand a little more about the chemistry of your 
system and the test methods you are using.
> On the subject of precision and sensitivity, my Hach catalogue claims that
> their Tannin/Lignin Test Kit (#1937-01) is capable of readings of from 0 -
> 15 mg/l with a sensitivity of 0.5. Are you sure that the LaMotte kit is 2X
> as sensitive and 2X as precise (see the details about the LaMotte kit I
> quote above).

I'm talking about the LaMotte water color test kit vs. the Hach water 
color test kit.  You need to use 1/2 increments of titrant to achieve the 
2.5 APHA color unit precision that the LaMotte test kit can give, again, 
the details are in my column.
> LaMotte's kit is around $58.00, but the HACH kit is $100.00.

Again, you are somewhat confused about what test kit I was describing. I 
meant the APHA water color test kit.
> > What is the optimal concentration of humic acids for freshwater systesm? 
> > That is an open question, and your data can help answer that question.
> That wasn't my question. I would like to know what the concentration of
> Humic Acids and Tannins are in blackwater biotopes IN NATURE. 

Then go look it up or take a field trip.  I'm more interested in the humic
acid content of successful planted tanks (or water color in APHA color
units) because the background work that I've done on humification in reef
aquaria vs. nature hasn't been done for planted tanks vs. nature, at least
to the best of my knowledge. 

You are really deluding yourself if you think that the content of 
phenolic groups in humic acids in blackwater environments is the same as 
in a freshwater planted tank.  In the former case, most of the phenolic 
groups in humic acids are derived from terrigenous lignin.  In the latter 
case, it is mainly derived from fish food.  I don't see any reason to 
believe they will be the same.

But you know, as long as the test kit reads in mg/L, bada bing, we have 
analytical thinking/methodology.