I have a 30 gal hex also and speaking from experience I can give you a few pointers. First, although 30 gallons seem like a decent size tank you have to remember most of it is in the height. You don't have a whole lot of ground area, especially after you get done planting it. I wouldn't recommend too many bottom dwellers or they will be fighting over territory. That said also remember you don't even have as much length as even a 20 gallon so schooling fish are not going to have much room to "school" side to side. Find yourself a nice mix of bottom, middle and top dwellers. You'll have activity in all depths of the tank and crowding or territory fights will be kept to a minimum. If you plan on planting the tank you will realize Giant Hairgrass is your friend. It makes a great background in a narrow but tall tank.