Humic Acids

If you all pick up an iddue of AFQ from a couple of issues ago, you will 
find what I wrote about humic acids in marine/reef systems, some of which 
will be partially appicable to your needs.

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.  

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.

There are a number of chemistries for measuring the phenol content of 
water.  Almost all of them work at high pH, and there is a big problem 
with magnesium crashing out of solution when any of these chemistries are 
run in a marine matrix.  This should not be a problem for most of you in 
your freshwater tanks.  Yes, you will be able to measure humic acids 
colorimetrically in most cases.  At least if your aquaria are typical.

What is the optimal concentration of humic acids for freshwater systesm?  
That is an open question, and your data can help answer that question.