The meter reads the recipe. Pattern first, bottle last.
Burnt tips, but my EC and pH look right. What's going on?
GROWER ANSWER
Your meter tells you what went in. The plant tells you what happened after that. A feed that reads fine in the bucket can hit harder at the roots when the pot dries back hard, the air is dry, or the light is pushing her. And a leaf can look short of calcium when the calcium is in the pot and the air just isn't moving water through the leaf.
Pattern first, bottle last.
The recipe isn't the meal
The number on your pen is the recipe. The roots eat whatever the pot turns that recipe into. When a pot dries back hard, water leaves faster than the salts do, so the mix around the roots gets stronger between waterings. When the air is dry or the light is strong, the plant pulls water harder, and the salts it carries pile up at the leaf tips and edges first. Same bottle, same pen reading, a hotter meal.
Read the pattern
Just the very tips, the rest of the leaf healthy green, and it isn't spreading: often a plant running near her limit. Watch the new growth first.
Tips plus crispy edges, worst on the top leaves or the side facing the light: most often the room making a normal feed hit harder. Look at heat, dry air and light first.
Spots or twisted new growth in one part of the canopy, near a fan or in a dead corner: the air may not be moving water, and the calcium in it, into those leaves. More on that below.
Yellow climbing from the bottom up: usually hunger or a pH lockout, not burn. See How can I tell when my plant wants more food?
Run it in this order
The pattern. Use the list above.
The room. Point an IR thermometer at the top leaves. Under LED they should read 1 to 4°F below the air; at or above the air, the leaf has stopped cooling itself. Air below about 40% humidity, or a canopy at 84 to 86°F, makes any feed hit harder. And the air should move gently through the canopy: leaves moving, not whipping.
The root zone. Lift the pot. Water when it's noticeably lighter, to 10 to 20% runoff, instead of letting it go bone dry between waterings.
The runoff trend. Runoff above the feed is normal: about 1.2 to 1.5 times the feed. Up to about 30% above needs no thought, and the rest of that range is still normal. What matters is a gap that keeps climbing 2 to 3 waterings in a row. In soil the numbers are looser, so lean on the trend even more. Normal runoff with burnt tips points back at the room or the watering. A climbing gap means salt is building.
The smallest correction. If salt is building, trim the feed 10 to 20%, or give one watering of plain pH'd water or a very light feed (half strength or less), then let it dry back. If it isn't, change the room or the watering, not the feed.
Why more cal-mag often isn't the fix
Calcium rides into the leaf with the water the plant moves. If the air is still, damp in one pocket, or blasting one side, the newest leaves can show a calcium problem with plenty of calcium in the pot. Adding more to the bottle doesn't move it. Fixing the air does.
The exception is the water itself. Reverse osmosis water and rain water start with almost nothing in them, calcium included, so they need it added.
What not to do
Don't panic-flush. A big plain-water flush can swing the pH, leave her hungry and keep the roots wet for days.
Don't stack the fixes. Cutting the feed, flushing, adding cal-mag and moving the pH in one week leaves you nothing to read.
Don't judge the old tips. Burnt tips don't heal. Judge the new growth: the first signs show in one watering cycle, and the verdict takes about 7 to 10 days.
When it's something else
Bleached or curled tops right under the light: see Tacoing or bleached tops: is my light too close?
A runoff number that scared you: see My runoff number is high. Should I flush?
Reverse osmosis or rain water: see What water should I use, and what pH should it be?
On our shelf in Worcester: EC and pH pens and calibration fluids are in pH, water & meters, and clip fans are in Climate, air & controls. Call (508) 459-9609 or get directions.
Keep going
Watch the episode: Why Tip Burn Happens When Your EC and pH Look Right on MyRemy Live.
Watch the episode: MyRemy Live: Burnt Tips Aren’t the Problem (Why Panic Fixes Ruin Grows) on MyRemy Live.
Watch the episode: MyRemy Live: Airflow vs Cal-Mag. Why Your Plants Look Calcium Deficient (But Aren’t) on MyRemy Live.
Choosing a pen: see our pH and EC meters shelf guide.
Pattern first, bottle last. The whole system for a steady grow is written down in the free Stability Playbook. Get the free Stability Playbook
More answers: all grow guides. Every shelf guide and maker feed chart: Grower Resources.