Using your artificial lights or water flow as a source of energy is a poor investment. Nothing is 100% efficient. Aquarium lights do not give enough intensity to make significant energy with solar panels, let alone the fact that you would be blocking light and then converting it at 30-40% efficiency back into electricity. While putting a little turbine on your outlets will generate power, you need to take into account the increased load that will put on your pump and the reduced flow to your tank either in terms of g/hr and/ or speed of the flow. You would generate a few watts at best, only enough to power 2-3 low luminosity LEDs.
Now if you want to install solar panels or a mini hydroelectric plant from a natural source, you can make some significant gains for powering your aquarium.