That's a good question if you get one you will have a shadow on each side if you buy 2 the units will be approx. 2 inches longer than the tank.. I have 2 dimmable 120 watt with 90 degree optics on my 55 gal
. if you get one without optics it may not have shadows but light wont penetrate as deep. I don't know how deep you tank is but mine is approx. 20 inches. With the 120 watt Taotronics LED
units you can grow practically anything I have a clam on the sandbed that is doing great and I had to move my star polyps into the middle of the tank because of the intense light... call and talk to this guy he knows his stuff about the leds he sells. I bought mine with a 1 year warranty, 2-120 dimmable units for $300 he will tell you what you need for your tank Greg Huddleston 918-629-1402.
This is what I got for $300 2 of the units in the link with 90 degree optics if you don't understand optics he will explain it to ya....http://www.ebay.com/itm/28blue-27whi...item35c22ca6ad