I actually did DIY CO2 on a 155 gallon tank, with two gallon jugs. Couldn't grow everything I tried, but it was good enough to do this: https://www.flickr.com/photos/[email protected]/16971910918/ Swords, crypts, ludwigias, vals, bacopa were no problem. I've since upgraded, but threw away or sold plants many times over using DIY in a big tank.