The library gives a homemade route for humic acid and a rate for the IMO3 recipe. It names no commercial product and gives no humic acid ratio for an IMO4 batch.
To make humic acid from worm compost, steep the worm tea like a teabag until it turns dark brown. (Office Hours Ep. 136, 37:26)
One office hours recipe brews IMO4 bubbler tea by bubbling a handful of IMO4 with a handful of IMO2. It adds maintenance solution and worm humic acid, and brews about 36 hours. (Office Hours Ep. 107, 25:32)
Cho's IMO3 substrate recipe lists humic/fulvic acids at 1:1000. (Cho's Solutions, p. 18)
For stored IMO4, Drake says it holds up to freezing in spore form if it is fed food, minerals, and humic-fulvic acids before spring use. (Office Hours Ep. 15, 46:33)
Sources
