Have a fairly new 29 gallon freshwater tank at work. Using 72 watts total lighting. 2 ea. 6700 k bulbs and 2 ea. colormax bulbs. Substrate is CaribSea Floramax. Run the lighting 7 hrs per day. The plants are beginning to develop brown spots on the leaves. My Cardinal Plants (Lobelia cardinalis) are the hardest hit. Is this a CO2 problem or does the substrate lack the micronutrients to fully sustain the plants?