More to the point, these hang-on-tank refugiums are really too small to be very effective. Save your money or return it and get a refund. It you still want to add one, think of it as a "looks nice and seems good" kind of product.
These hold about 2 1/2 gal or about 5 gal depending upon the size you get. Do you really want a dead weight of about 25 lbs or 50 lbs hanging on your tank? Even though it is said to hang on the tank, I'd also support it from the bottom.