I have the Eco Pico Arm and yes it is wider than the tank if you put it on the back. I have mind on the side (ends) of the tank and is just perfect. It hits the whole tank that way.
I also ordered the extra two strips for a total of 3 is all you can fit on this arm. So far love the light alot.
If you do get it make sure when you are connecting the three lights into the main extension you give them a good push to hear the click otherwise you will not get full power on the lights like I did (stupid me...
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