I've read the excellent guide: Algae-Scrubber-Basics-The-Summary
Tank size: 30cm3
1 litre = 1000 cubic centimeters
1 US Gal = 3.78541 Litres
1 Inch = 5.08cm
((30*30)*30/1000)/3.78541=7.13 US Gal
1. Advice from guide is 1 watt per 1 gallon so it's more than sufficient to use a 10 watt LED as below?
http://item.taobao.com/item.htm?id=10584760366
2. So my screen size should be;
2-inch^2 = 4
7.13-Gal * 4 = 28.52-area
ratio of L:W (2:3)
28.52 = 3x * 2x
6x^2 = 28.52
x^2 = 4.75
x = sqrt(4.75)
x = 2.1
L = 2 * 2.1 = 4.2-inch
W = 3 * 2.1 = 6.3-inch
L = 4.2 * 2.54 = 10-cm
W = 6.3 * 2.54 = 16-cm
correct?