Generally speaking, you want to have as little algal buildup as possible. Algae thrive in areas with a lot of light (from the sun or a bulb), but they also use much of the oxygen that would typically be available for your fish. To reduce the likelihood of growing algae, ensure all tubing and tanks in your system are black or opaque so they block as much light reaching the water as possible. This sometimes also means covering your fish tank as much as possible, while still leaving room for oxygen to enter.