Fox Farm recommends that you do not use Grow Big along with Ocean Forest Soil. Ocean Forest is very hot, and has plenty of nutrients in it for a long veg. They recommend feeding with Big Bloom (not Tiger Bloom) during veg to give the plants a lot of good organic NPK. Grow Big and Tiger Bloom are not organic nutes, by the way. Big Bloom is the only fully organic nutrient in their line.
So, I would say that you should only feed Grow Big if they show signs of nitrogen deficiency. If your old leaves begin to fade to a yellow color, it is time to give them a small bump of nitrogen (Grow Big). Underfed plants can be quickly and easily repaired with a light feeding. Overfed plants will be horribly stunted, and will take quite a bit of time to heal. It is always good to be on the safe side.
So, in summary, feed your plants when they need it. Always go on the light side. I have had serious burn with Grow Big and Tiger Bloom when using the recommended dosage. Think of light nutes as vegetables for your plants, and strong nutes as cheeseburgers. The cheeseburgers may fatten them up, but they will not be as healthy. Take it light, and always watch your pH. The pH of FFOF soil is pretty good, but when you start to mix full strength nutes, it can knock your water pH into the low 5s.
Happy Growing!
S-Town