I have just replaced my 61w fluorescent bulb with a new 18w Toshiba planted tank aquarium bulb (made in Thailand). The manufacturer said it has a special spectrum to promote plant growth- Watbrighter. Does an 18w is enough for my 65g tank? or should I keep with a 61w (normal fluorescent bulb). My tank receive some sunlight in the morning about 2 hours - I should not actually but space is a concern.:help: