I am growing in Hydro and I have added Molasse to my res (way over 60gl as Toke has suggested) and the water is circulating all the time (one pump mix the nutes inside the tank and one pump send the water to a water chiller, both pumps are on 24/7) and so far my plants love it. Probably the amount has to do with it, Hatch has recommend me just to use 1 to 2ml per gallon (one tbsp equal 7ml, and in soil most people use one or two tbsp per gallon)
I just wanted to add this info as I have read the same cncern with Molasse and Hydro in different sites, but I can assure your plants will love the Molasse
Regards