First off, I'd like to welcome you to Tropical Fish Keeping forum.
Now to your questions. The thickness of the planting in an aquarium should be generally governed by the fish, by which I mean their level of swimming activity. Your Cherry Barb
and Red Eye Tetra
are both lively fish that like space to swim. My suggestion would be a couple of common sword plants, Echinodorus bleherae
, toward the rear corners. The Pygmy chain sword
would work well everywhere else; a couple of these once settled will send out runners and cover the substrate nicely. You can see info and photos of both these species in our profiles section; second tab from the left in the blue bar at the top, or in posts click on the shaded name to see that fish/plant profile.
If you'd like either plant, since you are in Vancouver, drop me a PM. I have so many I am tossing them out; free if you come by for them.
I would stay away from stem plants, they require more light (prob why your cabomba kept disintegrating) plus being fast growers they need regular trimming/pruning. They also take up space. One of the nice things about sword plants is that the leaves fan out, and lively fish can swim around them, so you get the best of both worlds: nice plants filling the tank, but still "open" space for swimmers.
To the plants in your photo: right rear corner is Java Fern
, and you have it properly attached to a piece of wood (burying the rhizome can cause it to rot). The plant to the left and centre is probably a terrestrial plant and thus will not last long. Some stores do sell these as aquatic plants, but they are not. It will be OK as long as it is solid, but if you notice it start to yellow and turn "mushy" pull it out. The plant in the left rear corner is a sword, Echinodorus species, prob E. bleherae in its emersed form. [You'll find out what this refers to if you read our profile referenced previously]. If you take me up on my offer, I can give you half a dozen very healthy submersed plants.
Lastly for now, the light. One tube is adequate; what type is it? I recommend "daylight" tubes with a kelvin of around 6500K. They provide the necessary red and blue colour light that plants require to photosynthesize, plus some green to balance so the fish and plant colours are rendered true. You can get these in hardware stores for a couple dollars; GE, Phillips and Sylvania all make them.