Ok so the tank is my sons 20 long with no light no heater It currently houses 3 3 inch bull head catfish and at times some feeder guppies, he would like to put some floating plants in his tank. I know that water lettuce is ok for low light situations, the only light the tank gets right now is indirect sunlight, so the question is would water lettuce be ok or something like frogbit? any suggestions would be great! thanks in advance