Nutrifin Plant gro is a trace element mixture, not a complete fertilizer. It doesn't provide the nitrate and phosphate or the potassium needed by the plants. With 2 watts per gallon, unless that light is held well above the water level, you need to be dosing a complete menu of nutrients.

So, you need to get some potassium nitrate, for nitrate and potassium, and some phosphate, such as mono potassium phosphate, and dose those along with the nutrifin plant gro.