Eco Complete is fine with cories. I've used it and it's great for growing plants. You'll probably need 2 bags for your 29 gallon, as one bag is only 20 lbs. If you have normal output flourescent lighting, you may not need to go with Eco, since you will be limited to slow growing low light plants. When I used it I had a 130W power compact fixture over a 55 gallon tank and grew low and medium light plants quite well. You can mix Eco with gravel to save money if you want to.
A lot of the other members have already seen these pics, but here is my old 55 in case you're wondering what you can do with Eco and power compact lighting. It's the same tank, same lighting, just 2 different aquascapes. The substrate is 40 lbs Eco, 20 lbs natural colored gravel. I was pleased with the results.
