I have the lights on for about 10 hours a day, i actually get decent growth from all my plants including my new Giant Hygrophila and an Amazon Sword. You are correct that it is a tall tank. I did find something last night though, out of curiosity i checked my tap water and it shows 10-20 ppm of nitrates right out of the tap, so in a way i am adding some nutrients to the tank with each change over. Another factor is until a week ago i did have 2 goldfish in the tank and i know they produce Massive amounts of waste, it could be just cycling the excess out of the tank. Did a 20% water change last night and added a water clarifier and this morning it was much better, but left the lights off and put on a blackout towel for the day.