Run your tap water straight if it's about 250 ppm (0.5 EC, 500 scale) or lower. If it's higher, blend in RO to bring it down to about 250 ppm. For tap around 500 ppm (500 scale), a 50/50 tap and RO blend gets you there. Then mix the usual chart amounts.
Straight RO works too, with no Cal-Mag. Our Veg and Bloom formulas have multiple calcium sources built in.
Why we like some tap in the blend
Enough tap water in the blend cuts down or eliminates the need for pH up. Your water's alkalinity, not its pH, tells you how much adjusting the feed will need; see water pH, alkalinity and hardness. Mix the nutrients in completely, then pH the finished feed, about 6.2 for coco and peat. Regular pH down works, or use RunClean in its place.
Same chart amounts with any water
Keep the chart amounts and ratios the same with any water. Minerals in the source water aren't a substitute for one of the parts, but they do add to the meter reading. At chart rate, feed made with RO reads about 2.2 EC or a bit higher, and tap reads higher than that.
When you switch water, expect the EC number to move and leave the dose where it is. On injectors, compare a dripper sample with a hand-mixed batch made from the same water.
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