Well my hydro this year didn't go so well. I put a fogger into the coffee container that I made my hydro setup out of and it killed the plant. But hey it looked cool dying....lol I think the fogger may have done something to it only because the roots were to close or even on it. Im not sure but that is my guess. However once it was pretty wilted, I was unable to get it back so I tossed it. Maybe next year I will give it another shot but without the fogger. I want to do just one plant though because its easier to maintain one plus it allows me to focus on the success when I have just one and if ti fails I don't need to worry about failing miserably...lol
If you do or don't have a post already about your hydro, I would be very interested in seeing it and how things have been going. To answer your question, yes you can spray fish fert right onto the leaves. I did that with all my plants and they loved it. Just dont do it to much. I would say once a week to even once every two weeks would be plenty. The mixing of the spray is on the bottle. It will tell you how much to put into the water. I mixed it in a 32oz spray bottle and then shook it all up until it was mixed up well. Be careful not to get any of it on you. IT STANKS.