That's redfeild's eqn. It's the empirical algae formula that he based his #'s on. Clearly lacking the micros., which means other metabolic paths can result in algae...which i dont recall
I would really like to play with this some more, I've been having lots of luck with Ghazanfar's N:P of 10:1 which is very close to this ratio. Does anyone have a working phosphate kit? So far I've determined Salifert and Hagen PO4 kits are bunk. Are the Sera kits available in the US?
What people try to say is eliminate algae by making PO4 a limiting reagent. Works well for rationalizing the steps to remove DOC, P, N from the return to river from waste water plants. Prior to good removal of macros, I understand years ago the potomac near one of the bridges/waste water sites was a pretty blue-green sheet for most of the summer.
I think the #'s for plant tanks come from sources that study heathy ecosystems. Someone at aquabotanic's forum has hoarded these links, I've read a few of them.