Fox Farms' 'Grow Big' has two formulations, one for soil, one for hydroponics ... while you CAN use them interchangeably (I have), it is better to use them as defined ... I don't have the bottles in front of me now, but the soil version is 6-4-4, and the hydro version is something like 2-6-4 .. ??? don't trust my memory :jointsmile: