# Brown or dark speckling and bronzing on older leaves: likely causes and fixes

> Brown or dark speckling and bronzing on older leaves on cannabis is most often Manganese toxicity (usually low pH), Low root-zone pH starving calcium and magnesium or Iron and manganese excess at very low pH. How to tell them apart, the fix for each and what recovery looks like.

Also called: dark speckles on old leaves, brown freckles, bronze speckled lower leaves.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=brown-speckles-old

## Likely causes, most likely first

### Manganese toxicity (usually low pH) (Possible)

- Kind: Too much of something; urgency: Low urgency
- Fix: Raise root-zone pH into range (soilless 5.8-6.2, soil 6.2-6.8); check that the micro mix is not over-dosed. Tissue tests may not flag it: in one trial, symptomatic plants had normal leaf Mn.
- Recovery: Margin yellowing stops climbing within 7 days.
- Confirm: 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.
- 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: [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.md)

### Low root-zone pH starving calcium and magnesium (Less likely)

- Kind: pH; urgency: Deal with it this week
- Fix: Raise root-zone pH to range: coco 5.8-6.2, hydro 5.6-6.0, soil 6.2-6.8. Use pH up (potassium hydroxide or carbonate) in small steps; in coco, feed at 6.0-6.2 for a few waterings with Ca and Mg on board. A fast fall in hydro points to dying roots or microbes; check them.
- Recovery: pH holds in range for a week; new leaves spot-free within 7-10 days.
- Confirm: 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.
- 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.
- 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: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md)

### Iron and manganese excess at very low pH (Less likely)

- Kind: Too much of something; urgency: Low urgency
- Fix: Raise root-zone pH above ~5.5 (soilless) or 6.0 (soil); below about 5.3, Fe and Mn become very soluble. Cannabis Fe toxicity itself is not characterised.
- Recovery: No new speckling on leaves that develop after pH correction.
- Confirm: 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.
- Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth.
- Article: [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.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.