pH Lockout: Diagnose and Fix Nutrient Lockout

What pH lockout actually is

Lockout means essential elements are present in the medium but chemically unavailable at the root zone pH. Cannabis absorbs different nutrients at different pH levels — drift even 0.5 outside range and you get deficiency symptoms while the bottle nutrients sit unused.

Growers often respond by feeding more, which makes burn worse on top of lockout. Fix pH first, always.

Symptoms that scream pH before deficiency

Lockout mimics multiple deficiencies at once:

• Interveinal yellowing on new growth (Mg/Fe lockout)
• Purple stems and leaf edges with otherwise green leaves
• Brown spots appearing despite "correct" feed schedule
• Multiple deficiency patterns on one plant simultaneously
• Problems persist after increasing calmag or nitrogen

How to test properly

Soil: test runoff pH and EC after a normal feed — not plain tap water unless flushing. Input pH matters, but runoff tells you what's happening at the roots.

Coco/hydro: test input and runoff every feed until stable. Runoff pH should stay within 0.3–0.5 of input.

• Calibrate pH pen before every grow week
• Soil target runoff: 6.0–6.5
• Coco/hydro target: 5.5–6.0
• Record numbers — patterns beat one-off readings

Fixes by medium

Soil: flush with pH-adjusted water (6.0–6.5) at 2–3× pot volume if runoff pH is wild or EC is sky-high. Let dry to normal rhythm before resuming 25–50% strength feed.

Coco: flush until runoff EC drops near input levels. Re-feed immediately with correct pH — coco doesn't like sitting empty long. Add cal-mag to the next two feeds after a flush.

Prevention

Adjust pH after all nutrients are mixed — not before. Check runoff weekly in soil, every feed in coco. Replace pH probe storage solution and probes annually if readings drift.

Tap water with high alkalinity fights pH down — know your source or use RO with calmag replenishment.