No need to change it unless you have a problem. Mine are on for 8 hours. Before I reduced the intensity I could only manage 6 and still got some BBA - not enough to cause a problem but it was noticeable.I have been using flourish advanced to get them rooted. I have moneywort vallisneria,anarchis, pearlweed,and java moss. Should I lower the intensity of the lights and how long should I keep them on for those plants. Substrate is ecocomplete.