When plants share the same tank and only one looks wrong, the feed usually isn't the problem. Something about that one pot is different: it's getting less water, holding too much, has a root problem, or sits in different conditions. Test that pot next to a healthy neighbor before you change the whole tank.
Check delivery first
- Catch the water from the suspect outlet and a healthy neighbor's for the same run time.
- Look for a disconnected tube or a displaced emitter. A pot that's dry while others on the same zone got water missed a feed.
- Check the surface after irrigation. A dry patch or one dry side means poor coverage.
- Check the opposite too: a pot that stays wet and doesn't drain.
More on this in when part of a room misses an irrigation and getting every pot watered evenly.
Compare the two root zones
After a normal feed, catch the last 10% of runoff from the affected pot and the healthy one, and test each separately. Record the feed EC and pH, how much went in and came out, and your ppm scale. A pooled sample or a reading from some other pot can hide the problem. The method is in how to test runoff pH and EC.
Are you using microbes or a sterilizer? Tell us. Inspect the roots if you can do it gently. If a pot accidentally went dry, keep its readings separate from the rest.
Look at where it sits
Does it get more light than its neighbors, or sit closer to a fan? Was it transplanted later? Is its medium more compacted, or a different mix? Is it a different strain? Strains don't all run the same shade of green.
A photo of the whole plant and a close view of the new growth tell us more than one damaged leaf.
One plant, a few, or a row?
| Pattern | Look at |
|---|---|
| One plant | That pot's outlet, drainage and roots |
| One row | That row's hardware |
| One strain | Test that strain separately against a healthy plant |
| Scattered plants, same pattern | A shared zone, line pressure or source material |
If scattered pots show low runoff pH, unless you're going to go plant by plant and check every root zone, assume there are many plants with low pH and fix the room. One healthy neighbor doesn't clear the others.
Fix what you found
- Under-delivering emitter: repair it and catch-test again.
- Saturated pot: clear the drainage and lengthen the interval based on how fast it actually dries.
- Low runoff pH from buildup: pH 6.4 tap-water flush; the full steps are in Why Is Runoff pH Lower Than Feed pH?
- Environment: check that spot's air temperature, RH and measured leaf temperature in our VPD calculator.
Don't keep raising the whole feed, or add Cal-Mag, to fix one plant. Fix that pot, then watch its new growth over the next few feeds.
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