A&B nutrient mixing: order, compatibility, and reservoir hold time
A two-part A&B program is separated for one reason: concentrated calcium and concentrated sulfate/phosphate will react with each other and drop out of solution as gypsum. Kept apart in the bottle or bag and diluted fully in water before they meet, they stay in solution. Every rule below follows from that single fact.
Mix in water, never into each other
Fill the reservoir with your source water first, to at least 80% of final volume. Add part A, circulate until fully dissolved and the solution is clear, then add part B. Never pour A into B, never combine them in a measuring jug, and never stack them in a dosing line that has stopped moving. Cloudiness or a white sludge on the tank floor means precipitation has already happened and the nutrient your plants receive is no longer the nutrient on the label.
Where cal-mag and silica belong in the order
If your source water is low in calcium and you supplement, treat cal-mag as an extension of part A: it goes in first, dissolved, before part B enters the tank. Silica is the opposite problem: potassium silicate raises pH sharply and reacts with concentrated acids. Silica goes into plain water first, on its own, and is circulated and pH-corrected before any A or B is added. The universal rule is one additive at a time, fully dissolved and dispersed, before the next.
Dose to EC, correct pH last
Dose the base to an EC target rather than a spoon count, so seasonal shifts in source-water hardness do not silently move your feed strength. Take the EC reading only after both parts are fully dissolved and the tank has circulated. Adjust pH last: acid or base added mid-dissolution creates local extremes that push calcium and phosphate out of solution even when the final tank reading looks correct.
Water temperature and dissolution
Dry salts dissolve faster and more completely in water at roughly 18–22 °C. Cold water leaves undissolved crystals that either sit inert on the tank floor or dissolve later and spike EC unexpectedly. Warm water above the mid-20s accelerates dissolution but also accelerates biological growth in the reservoir. Circulate rather than heat.
How long a mixed reservoir holds
Plan on 5–7 days for a covered, circulating, temperature-stable reservoir, and re-check EC and pH daily rather than trusting the mix date. Drift upward in EC usually means evaporation; drift downward means the crop is drawing nutrient faster than water. An uncovered or warm tank should be treated as a 2–3 day mix. Keep the pump running: a still tank stratifies, and the first draw after a still period is not the solution you mixed.
Signs the mix went wrong
White scale on impellers and tank walls, a persistent haze that will not clear with circulation, a sudden EC reading below target after full dissolution, and emitter clogging in drip lines all point at the same cause: the two parts met before they were diluted. Dump, flush the lines with clean water, and rebuild the mix in the correct order rather than trying to correct a precipitated tank.
A repeatable procedure
Fill to 80% with source water. Circulate. Add silica if used, disperse fully. Add part A (with cal-mag if used), disperse fully. Add part B, disperse fully. Top to final volume. Read EC and adjust to the stage target. Adjust pH last. Log EC, pH, and water temperature against the date so the next mix is a repeat and not a guess.
