Pour the bottles of humic and fulvic acid mix over the SS when you are watering it for the first time in the tubs.
This will distribute the humic and fulvic acids decently. You'll still want to mix it again in a few weeks. This probably won't be as ideal as powdered form, but it should work. I think sub says to give 3 gallons of water for each garbage bin of soil, so Id say just mix that 3 gal h20 with however much humic/fulvic acid you wanna add per tub, and pour it over. hope that helps...i don't really know the difference between liquid and powdered humic acid in regards to efficacy, so maybe someone else out there will be able to shed some more enlightenment...
good luck