Stock Solution for an Injector

Feeding a large crop from pre-mixed reservoirs means mixing a great deal of water. An injector solves this by drawing concentrated stock into the irrigation line at a fixed ratio, so a 1:100 injector pulls one part stock into ninety-nine parts water, and the stock therefore has to be a hundred times the strength you want at the plant.

The two constraints that bite are solubility and compatibility. A stock at a hundred times strength approaches the solubility limit of several common salts, particularly in an unheated store where cold water holds far less — a stock that mixed fine in August crystallises in the tank in November, and the injector then feeds clear water while the fertiliser sits on the bottom. And calcium cannot share a tank with sulphates or phosphates at concentration: it precipitates as gypsum or calcium phosphate immediately. This is the entire reason commercial fertigation runs two stock tanks, conventionally A for calcium nitrate and B for the sulphates and phosphates, meeting only in the dilute irrigation line.

Verify rather than trust. Injector ratios drift with line pressure and flow rate, and a diaphragm injector that has done a season is often several percent off its nameplate. Check by running the injector into a measured volume and reading the EC of the diluted output against what the arithmetic predicts. That single check catches both a wandering injector and a stock tank that has quietly dropped part of its load out of solution.