Dull, grey-green, leathery leaves

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. PossibleSodium build-up (softened water, coco, recirculation)

   Too much of somethingDeal with it this weekRead: Sodium (Na) and cannabis: a salt to keep low, not a nutrient to add

   Fix: Never use ion-exchange softened water. Keep feed sodium below about 50 mg/L (more than ~5 mM NaCl, 115 mg/L Na, may cut hydro yield and cannabinoids fall as NaCl rises). Dump and refill recirculating reservoirs more often; rinse coco before planting.

   Recovery: Tip burn stops advancing on new leaves within a week.

   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.
   • Leaf tissue analysis. Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency.

2. PossibleSalt build-up in the root zone

   Root zoneDeal with it this weekRead: Runoff testing: how to measure root-zone pH and EC and what the numbers mean

   Fix: Root-zone flush: water slowly with pH-adjusted, quarter- to half-strength feed (not plain water in coco) to 20-30% runoff, about 2-3x the pot volume, until runoff EC is within ~0.3-0.5 mS/cm of input. Then water to 10-20% runoff each time. This treats the medium, not the plant; it is not a pre-harvest flush, which is a myth.

   Recovery: Runoff EC tracks input at the next 2-3 waterings; new leaves stop burning.

   How to confirm it

   • 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.
   • 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.
   • Slurry (1:2) test of the medium. Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like.

3. Less likelyChloride excess (salinity)

   Too much of somethingLow urgencyRead: Chlorine and chloride (Cl) in cannabis: a micronutrient you never need to add

   Fix: Keep chloride below about 50-70 mg/L in the feed; switch potassium chloride for potassium sulfate; blend high-chloride water with RO.

   Recovery: No new tip burn after the change.

   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

Matte grey-green canopy with thick leaves; include runoff EC..