If your plants look unhappy and you're feeding correctly, the problem is almost always pH or EC. Here's what the two numbers mean.
pH is the gatekeeper. Nutrients are only absorbable inside a pH window. Soil: 6.0-6.8. Coco/hydro: 5.5-6.5. Outside the window, your plant starves while sitting in food — that's lockout, and it looks like a deficiency.
EC is the strength. It tells you how much dissolved nutrient is in your water. Seedlings: 0.4-0.8. Veg: 0.8-1.4. Flower: 1.4-2.0. EC climbing day after day in hydro? Plants are drinking water faster than food — dilute. Dropping? They're hungry.
Measure every time. A decent pH pen and EC meter cost less than one lost plant. Calibrate monthly, store the pH probe wet, and write readings down — patterns tell you everything.
We carry calibration solution, storage solution, and replacement probes for every meter we sell. Bring your pen by the shop and we'll check it against ours.