EC and pH Adjustment

It compares your target EC to your current EC: if target is higher, it computes concentrate to add using a rough 0.3 mS/cm rise per mL of concentrate per gallon; if target is lower, it instead switches to computing how much fresh water to add to dilute the solution. Only one of the two amounts will be nonzero for any given pair of readings.

It uses V_add = V_current × (EC_current / EC_target − 1), which comes from the fact that mixing a fixed amount of dissolved nutrient into a larger total volume proportionally lowers its concentration. So if your current EC is twice your target, this formula tells you to add a volume of fresh water equal to your current reservoir size to cut the concentration in half.

The calculator uses 2.5 mL per 10 gallons per pH point for pH Down (typically phosphoric or citric acid) versus 3.0 mL per 10 gallons per pH point for pH Up (typically potassium hydroxide or silicate), reflecting that these are chemically different concentrated products with different real-world potency. Both rates then scale with your reservoir size and how large a pH gap you need to close.

It multiplies your EC in mS/cm by 700 to estimate PPM, but that's just one of several PPM conversion 'scales' (500, 700, and others) used by different meter manufacturers. A PPM reading from a meter built around a 500 scale will read noticeably lower than this calculator's output for the same actual solution, so compare EC readings directly rather than cross-checking PPM numbers between different meter brands.

Both the EC-to-concentrate and pH-to-solution ratios used here are approximations that vary by product concentration and brand, so the calculated amount is a starting estimate, not an exact dose. pH in particular moves on a logarithmic scale, meaning the same volume of pH adjuster produces a much bigger swing when you're already close to neutral than when you're far from it — so always mix, wait, and re-measure with a calibrated meter before adding more.