I've been using phDown (phosphoric acid) for a few years, and have never had a problem. Well, except for a few months ago when I mixed 5 gallons worth in a gallon jug. Kinda pissed-off the ladies, but a quick flush and all was good.

Anyway, I have 7.9 to 8.0 ph wellwater and use 1/4 tsp:gallon, bringing my ph down to around 6.7-6.8.

A former troubleshooter in here (stinkyattic) did the math for me a couple of years ago, and at my dilution rate she thought I was fine. She's a chemist familiar with such chemo-numerical mumbo-jumbo.

The thread is around here somewhere...AH HAA...here it is, but don't let the title fool ya:
Humic Acid...
Rusty Trichome Reviewed by Rusty Trichome on . PH down= phosphorus toxicity? Im trying to figure out a leaf curl problem and talking to my guy at the hydro store we were going over some possibilities and he mentioned something about adding phosphoric acid may lead to too much phosphorus in the solution anyboby hear of this?:hippy: Rating: 5