# Runoff EC well above input EC: likely causes and fixes

> Runoff EC well above input EC on cannabis is most often Nutrient burn (feed too strong), Salt build-up in the root zone or Sodium build-up (softened water, coco, recirculation). How to tell them apart, the fix for each and what recovery looks like.

Also called: high runoff ppm, runoff EC high, salt build up, runoff higher than input.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=runoff-ec-high

## Likely causes, most likely first

### Nutrient burn (feed too strong) (Possible)

- Kind: Too much of something; urgency: Low urgency
- Fix: Drop input EC by 0.3-0.5 mS/cm (or to about two-thirds strength); seedlings and clones need 0.4-1.0 mS/cm. Soil with pre-loaded nutrients usually needs plain pH-adjusted water for the first 2-4 weeks. If runoff is far above input, do a root-zone flush (see salt build-up).
- Recovery: No new tip burn on leaves that open after the change, within 5-7 days; burnt tips stay.
- Confirm: 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.
- Confirm: 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.
- Article: [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md)

### Salt build-up in the root zone (Possible)

- Kind: Root zone; urgency: Deal with it this week
- 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.
- Confirm: 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.
- Confirm: 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.
- Confirm: 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.
- Article: [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)

### Sodium build-up (softened water, coco, recirculation) (Less likely)

- Kind: Too much of something; urgency: Deal with it this week
- 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.
- Confirm: 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.
- Confirm: 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.
- Confirm: 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.
- Article: [Sodium (Na) and cannabis: a salt to keep low, not a nutrient to add](https://genetixbay.com/knowledge/nutrients/sodium.md)

### Uncalibrated or failing pH or EC meter (Less likely)

- Kind: Physical damage; urgency: Deal with it this week
- Fix: Calibrate the pH meter with fresh pH 7 then pH 4 buffer before decisions and at least weekly; store the probe wet in storage solution, never in RO water. Check EC against 1.413 mS/cm. Replace probes that won't calibrate (typical life 1-2 years). Drops and strips are too coarse to diagnose with.
- Recovery: Readings match the buffers within 0.1 pH; the 'problem' pH disappears or is confirmed.
- Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter.
- Article: [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)

### Cal-Mag overuse (excess calcium and nitrogen) (Less likely)

- Kind: Too much of something; urgency: Low urgency
- 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.
- Confirm: 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.
- Confirm: 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.
- Article: [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md)

### Excess phosphorus (bloom boosters) inducing Zn, Fe and Ca shortages (Less likely)

- Kind: Too much of something; urgency: Low urgency
- Fix: Drop the booster. Keep P at about 30-60 mg/L; four controlled cannabis trials found no yield or cannabinoid gain above roughly 25-60 mg/L, and excess P just leaves in the runoff.
- Recovery: New growth greens within 10 days of returning to a balanced feed.
- Confirm: 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.
- Confirm: 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.
- Article: ["Bloom boosters" for cannabis: what's real and what's marketing](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md)

## Note

Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth.