You are right. Tht PH down will work fine. Apply it at half the rate you think you should. Since this a a largely unknown product in your situation I'd go about 7ml or less for the tank and then see what that does. It should be equivalent but you have to check to make sure.
COOL!
I just used 7ml into 1/2 gal and mixed and poured into the unit.
How long before getting a good reading?
With the 1 gal AG unit I waited 1/2 to an hour. How long should I wait with the 6 gal tub?
Is it neccesary to mix the 1/2 gal with my hands in the tub or the pump and bubble are enough?
Sorry for all the questions, This has been one hell of a ph roller coaster ride.