[jeff5may]

For larger systems, I usually start off with rainwater, Epsom salt, and ag phosphate acid. It comes in bags like ag lime. Add some chalk or ag lime for calcium hardness. I mix up a bucket of tap water to around 1500 to 2000 ppm and balance ph to 6.0 with phosphate or lime. A gallon of this stuff will buffer 100 gallons or more rainwater and cost like 30 bucks for an Olympic swimming pool worth.

For small systems, I use tums and miracid to balance the rainwater. Yup, Kmart gro for acid loving plants is cheaper than solid ph down powder...After the water is buffered and balanced, nutrient is added at the prescribed "weak" rate and ppm is measured. If It's above 600, I add pure (rain or distilled) water to bring it down.