Hey Chris,
I've seen folks recomend 'as much as' a quart to 250 gallons. I don't know if I used that much when I 1st started...? I did the guy thing...I shook the bottle and poured some in and said ......that looks good...
Don't freak when you add some...the stuff is really dark and it will stain your water. (and it'll stain your clothes too) Your water will eventually be stained anyways.

You can always add more to the water over time..or...I also spray my plants with a weak mixture of maxi crop and molasses.

You can put the plants and maxi in the system, before the fish...or at the same time.