I'd like to try my first planted tank. I have a perfecto 20g with an 18 inch fixture. I bought a 15 watt, 675 lumen, 9322K light for the tank. The light says "will support plant growth in any tank less than 24 inches tall". The light was only $5 so I decided to try it. I know that .75 watts per g is really low, but what would be good beginner plants for such low light conditions? Another question, are cories fine for a planted tank? Finally, are any additives or CO2 necessary for this tank?