clarification from before: "I fill a tub with [40f, pH 7.1 @280ppm well water, then buffer with phosphoric acid to] pH 5.5 and let it mix and warm to 68f for 12+ hours.... by the time I get to it the next day, the pH is 6.2 or so which is [a perfect place to start, because now the water is warm and pH buffered].... after I mix the [warmed and buffered] water with ferts I get a rock solid pH 5.9."
Makes more sense now?