I think what may be happening is that phosphate ion is being actively transported across the root cell membrane and in order to maintain charge neutrality, hydronium ion goes with it. Since plants are phosphorus hogs during flowering the net loss of hydronium in the rez solution increases the ph. Adding phosphoric acid not only decreases the ph again but replenishes phosphorus.
I always wondered why lower ph's are recommended for hydro since phosphate is more available to plants at higher ph's. My theory is that the low ph actually inhibits bacteria growth which is more important than phosphate availability which can be compensated for by bumping up the EC with a bud booster type product.
I always wondered why lower ph's are recommended for hydro since phosphate is more available to plants at higher ph's. My theory is that the low ph actually inhibits bacteria growth which is more important than phosphate availability which can be compensated for by bumping up the EC with a bud booster type product.