use of humic acid in aquaria

 Bill Warner <lww at ictech_com>
 Craig Bingman <cbingman at netcom_com>
 Dave Huebert <eworobe at cc_UManitoba.CA>

and all who responded concerning humic acid; thank you!

Humic acid is available from hydroponics outlets; I got some for
about $2/lb. Would this be a useful addition to a new substrate?
What is an "ideal" proportion of humic acid in an aquatic soil?
Is there a danger if one uses too much? (presume yes since it is
an acid) What's the pKa for it?

Is there enough humic acid in ordinary dirt, loam, earthworm
castings or well composted manure mixed with soil that one doesn't
need to be concerned with supplementing it? Or is it only used
or needed in soil-less horticulture like hydroponics?

It sounds as if these organic acids play more of a role in plant
nutrient uptake and metabolism than "just" chelation. Are they
involved with other cations such as Ca & Mg? Are they important
for processes where EDTA, DTPA or EDDHA would not work?

When peat is used to remove hardness from water, is it the humic
acid which is performing this? How does it work?

Steve in Vancouver BC