The thing with the WPG
rule, is taht for smaller tanks, you need alot more. i.e. people with 10 gallons need up to 10 WPG
to keep things that you can do with 5 WPG
over a 100 gallon tank, and people with 2-3 gallon tanks may have as much as 15-20 WPG
Whereas on really large tanks, less WPG
Another MAJOR factor is tank construction. Shallow tanks do not need as much WPG
, where as a very tall tank would need what seems like excessive WPG
to create the same light intensity at the lower lvls of the tank.
The best way to determine lighting needed is to go by personal experience of other people with a tank of approx the same dimensions.