White scale on pots, pumps, drippers or the meter

Likely causes, most likely first

Ranked for this sign on its own. Your stage, medium and readings change the order, so run the checker for your plant.

1. PossibleHard, alkaline water pushing pH up over weeks

   Root zoneLow urgencyRead: Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine

   Fix: Alkalinity, not water pH, drives the climb. Above about 100-150 mg/L as CaCO3 (2-3 meq/L), neutralise most of it with acid to an input pH of 5.8-6.2, or blend with RO water. Track runoff pH weekly.

   Recovery: Runoff pH stops climbing over 2-3 weeks.

   How to confirm it

   • Get a water report (or test your water). Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium.
   • Measure input pH and root-zone (runoff or reservoir) pH. Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend.
   • Pour-through extraction for container pH and EC. Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable.

2. Less likelyCal-Mag overuse (excess calcium and nitrogen)

   Too much of somethingLow urgencyRead: Cal-Mag: what it is, when you need it and when you don't

   Fix: On hard tap water with a complete base feed, stop the Cal-Mag supplement; it adds N and pushes K and Mg out of balance. Use it only for RO or soft water and unbuffered coco. LEDs do not create a Cal-Mag need.

   Recovery: K and Mg symptoms stop spreading within 7-10 days.

   How to confirm it

   • Get a water report (or test your water). Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium.
   • Measure runoff EC against input EC. Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed.

Look for

Chalky deposits on reservoir walls, emitters or kettle-style scale..