There have been studies that compare growth rates in various conditions re: NO3 and PO4...high NO3/low PO4, low NO3/low PO4, low NO3/high PO4, high NO3/high PO4.Just curious why you state this, to be lower on NO3 vs PO4?
The lowest growth rates were always in the low PO4 conditions.
I can’t remember if the study discussed why. My guess is that if the NO3 and PO4 are utilized by the zooxanthellae, and growth rates are a function of the overall health and photosynthetic rate, then PO4 is going to be the more important limiting factor.
Algae will use NO3 to get ahold of the N, but it’s actually more energetically efficient to get the N from NH3...and I think they can get NH3 from that which is produced by the coral (don’t quote me on that last part)

