I know nuttin and told the store so, .After spending $1,300 and acting totally under advisement from the store,I used the Grow Big soil version on several grows AT FULL STRENGH they even sold me refills of the same product 3 times!. . Each time my plants crashed and burned. I was using Grow big soil this is what the "experts" at the grow store "set me up" to fail with so to speak.. It would have been nice to be given a "heads up" or see a note about using a reduced dosage such as use only 50% if growing Hydro. I understand even Fox Farm does NOT recommend using this product for Hydro grows (I know, I called em). I guess you could use it in a pinch, for a short time but far less then full strength.In a soil grow, this product I understand would work great in soil as I now understand the soil acts like a "buffer". I will order the Hydro stuff next time. why do you suppose they sold me a Hydro set up 100% and then supply the wrong newreants is this what our University's are putting out these days after all, customer service is everything. Now, if only I can get my wife to bring me a cold beer on the couch and go outside to to wax the car...... I guess we all can all only dream.