On Thu, 11 Jan 2001, I wrote: > If you want nitrogen-limited conditions and have 5 ppm NO3, then you > shouldn't let PO4 exceed about 0.2 ppm. What I *should* have said is: If you want phosphorus-limited conditions and have 5 ppm NO3, then you shouldn't let PO4 exceed about 0.2 ppm. Roger Miller