Recently, in the typical American thinking of “more is better,” I’ve come across people using upwards of 5 watts per gallon on their planted tanks. While it is possible to manage such a system, it is more work. I have yet to meet a “high intensity” plant that could not be grown well in a tank of normal depth at around 3 watts per gallon. If the plant is not growing at 3 watts per gallon, look to other causes for the failure first.