I agree, with one caveat. The tube itself can affect this. I did specific experiments with some tubes on my 29g, which takes a single T8 24-inch length. The low and moderate light plants did well with a Life-Glo tube; but with a GE Daylight they failed and actually began dying after a few weeks. Same with one of those so-called "plant" types; they are simply not strong enough (intensity). I had a cover of floating Water Sprite with all tubes as well, and regular fertilization was the same.I have a 24" T8 over my 29 gallon tank with floating plants (which is Frogbit now) and my plants below do fine. In fact without the floating plants I have problems with getting algae on the leaves of my Anubias. A 20 long is shorter plus I believe a T5NO is a lil bit brighter so I see no reason you couldn't have floating plants and be alright.