Can anyone tell me if two 56 watt led lights are enough to grow grasses in an 18" deep tank. I am running Co2 on a cycle with the lights. the watt per gallon is 1.7. seems a bit low to me but my aquarium store owner assures me that it is good enough. However the ground cover I put in the tank promptly died which may have been related to a low kh that I have now adjusted. Thank you in advance for any assistance.