Do you have 4-54 watt T5HO bulbs lighting the tank? 3 watts per gallon times 72 gallons equals 216 watts. If so, you most likely have enough light that you absolutely need to run the maximum concentration of CO2 in the water every day to avoid algae problems. This is done by increasing the bubble rate a little bit at a time, then watching the fish behavior for a day to make sure they don't all head to the surface and gasp for "air". Meanwhile, watch the plants for good pearling, which they should do if you have good CO2 concentration in the water. The goal is to get the pearling but not the fish distress.
Then, you need good water circulation throughout the tank to get CO2 to all plants all over the tank. This can be difficult, but is essential also.
Finally, the plants will be driven to grow very rapidly by that much light, so they need fertilizing at a rate so that none of the fertilizers is limiting the growth. I don't think that can be done by dosing only once a week.
You have a great aquascape, by the way!