I would suggest moving the spray bar to the end of the tank, on the left side there is fine, so it is along the end wall. Then turn to holes to face the wall. This creates a gentle flow down the wall and across the tank, and it also breaks the surface slightly. You can vary the latter by fiddling with the angle of the holes so it will have more or less surface movement. This positioning of the spray bar will create a slight stream current down the tank, very natural for the fish. Your filter intake is at the opposite end (right side), perfect.
Stem plants wold probably be the best for what you asked, although the light may be an issue. And speaking of light, it may have been part of the issue with the Vall and cabomba. There is not much red in 10000K. You might want to consider a tube around 6500K. You can buy inexpensive ones at hardware stores, Phillips make them (they call it Alto Daylight Deluxe 6500K) and Sylvania too. Just get an 18-inch T8 tube in this and I think you'll like the difference. The fish and plant colours will be natural, and the plants should respond even better.
One good stem plant that manages with moderate light is
Brazilian Pennywort; click on the shade name to see its description and photos, in our plant profile section. It would fill in nicely and grows up straight when rooted in the substrate; it also makes an excellent floating plant if allowed to float on the surface.
Byron.