plant?

What wattage and Kelvin (light temperature ex: 6700K) are the bulbs, do you know? I've read that T-5s put out quite a bit of light, and a 6g is teeny, so I'm guessing you'll have good light on the tank.
Make sure you research the plants - some that are very small in the store get HUUUGE when you give them good conditions at home! If the light is low, there are still plants that will stay small or grow slowly and do well like Java fern, some Crypts, Java moss and I know there are a few more as well.
 
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