How long do you leave tank lights on? When should you turn them off? leave mine on for 10-12 hours for the Amazon plants that I have but am seeing my decorations and gravel getting discolored. Only have the tank set up for 3 months, fully cycled. I also have a sponge filter that a friend gave me to keep my cycled tank seeded. Could that also be a problem with algae? It is a 20 gallon tank with 3 platys, a Top Fin filter, large airstone, live and artificial plants.