Join Date: Feb 2004
Location: Calgary, Alberta, Canada
Keep in mind that 18 LEDs over a 20L will look like a fiery inferno. I put 52 LEDs over my 6'x2' tank and before I put optics on I couldn't watch tv in the same room. That's with the LEDs running at less than half power.
Not saying you don't want all 18, just saying there probably won't be really noticeable dark areas.