THIS THREAD APPLIES ONLY TO THE FIRST VERSION OF THE L2 ALGAE SCRUBBER Most Rev 1 diffusers were shipped with sections that were blacked-out with a sharpie marker. The sharpie will fade over time, especially right in front of the blue LED. Instead of re-applying with a sharpie, use black electrical tape. Apply the tape on the smooth side of the diffuser. First, toward the middle of the bottom edge of each diffuser, apply 2 pieces of tape, each about 2" long - these will cover up the gap between the stand-offs on the inside of the box, and help reduce algae growth around the bulkhead drain. Second, apply a small square of tape (about 1 cm on a side, or the width of the tape itself) on the diffuser right in front of the blue LED. It helps to lay the heat sink on a flat surface and place the diffuser over it, so that you can place the tape in the right spot.