WOW that tank is gourgeous. thats an amazing red you got on it
Well, the tank has only 1.8 w/gal and the light is about 16" over the top, it's the plant and good CO2 that is the main cause.
Some species/variants stay nice and red.......it's not much of a trick to have nice red plants. If other folks thought it is a typical Ludwigia repens...then they'd feel pretty bad....but it's not.