i would recommend no more than one table spoon per gal to start with be-careful with the N while you're in flower its pretty much what ever work for you and your plants. you can add more depending on how your plants react make sure your ph is where your need it i would recommend no lower than 5.5 and no higher than 6.2 if you drift to far off your plants could still look relatively healthy but in reality there not. its just a game you have to play with them and you find out what they like and what they don't like. you can also try a leaf spray be very carful with that though and start off at a very low doss. let me know if you have questions