ph changes due to Co2

[sinistral]

Plus Takashi Amano grows high demand plants in big tanks with low lighting, and look at the dutch!!

There isn't a straight linear relationship between tank size and lighting. Amano uses very intense light for smaller tanks (8-10 watts per gallon for 5-15 gallon tanks) and uses much less intense light for larger tanks (less than 2 watts per gallon for tanks larger than 100g).

Here is an article which describes this relationship, with a java calculator at the end to compare your own tank to his.

Here is a second webpage saying the same thing.