How to mix A and B hydroponic nutrients without lockout
Why two and three part nutrients ship in separate bottles, how to add each part safely, and how per gallon dosing scales to any reservoir size.
Why nutrients come in separate parts
Two and three part lines keep certain ingredients apart in the bottle for a reason. Calcium from one part and sulfates or phosphates from another will bind into solid precipitates if they meet at full concentration, a chalky sludge that drops nutrients out of solution. By splitting the formula, the maker lets you dilute each part into the full reservoir first, so the reactive ingredients only ever meet at a safe low concentration. This is why the label gives the same per gallon rate for each bottle rather than one combined dose.
The correct order to add each part
Always add parts one at a time into a reservoir already full of water, and stir well between each. A common sequence for a three part line is micro first, then grow, then bloom, but follow your specific label since brands differ. Never pour two concentrates together in the cap or a measuring cup, and never add a part to a nearly empty tank. Once every part is stirred in, the calculator's per part figure tells you exactly how many mL of each bottle to measure so all parts land at the same rate.
How per gallon dosing scales
A dose written as mL per gallon is linear, so doubling the tank doubles the concentrate. If a label says 5 mL per gallon and you mix 50 gallons, each part needs 250 mL, and a two part set needs 500 mL in total. Switching to liters changes nothing about the chemistry, it only converts the volume: 100 liters is about 26.42 gallons, so the same 5 mL per gallon rate would call for roughly 132 mL per part. The tool does this arithmetic and rounds to two decimals so your measuring is practical.
Check the result with a meter
Label rates are a solid starting point, not a guarantee, because source water already carries dissolved minerals. Tap water with a high starting EC leaves less headroom before the mix gets too strong, while reverse osmosis water starts near zero. After mixing and stirring, measure EC or PPM and compare against the target for your crop and growth stage. Seedlings and leafy greens usually run lighter than fruiting plants in peak bloom, so treat the calculator output as your baseline and fine tune from there.