The general role for humic acid is to create chelated complexes that the plant can uptake various metals which act as micro nutrients. The hydroponic micronutrients are usually formulated with a variety of chelated metal compounds already. Read your nutrient label.
The "hydroponic" humic acid I have used as well. It tends to stick inside the DWC buckets and becomes a mess fast. Not worth messing with IMO
gotta agree with br26. plus it stains your roots so much that you can't tell if your developing a root problem. fulvic acid works muck better. it chelates minerals just as well as. mbferts has a good deal on fulvic acid powder