Excellent question. Didn't check.
Without knowing the alkalinity, it might be pointless to add fertilizer because if the alkalinity isn't over 20 (bare minimum) then the phytoplankton can't utilize the fertilizer. I'd much rather see ponds with an alkalinity of 40 as a minimum, that way there is a bit of a leeway before they drop too low. Just the same as adding lime to the soil to allow the plants to utilize the fertilizer in the soil.
Liming Ponds for Aquaculture
