What it is
Too much fertilizer. Nutrients are salts: when there are too many in the soil, they "suck" the water out of the root and build up in the leaf tips, which burn.
How to tell
The leaf tips turn yellow, then brown and crispy. The plant is usually a very dark, shiny green, with the leaf tips bent down ("clawing"). If it is severe, the burn spreads along the edges.
What to do
Flush the soil: water with a lot of plain water (2 or 3 times the size of the pot) so the water running out the bottom carries the salts away. Then let it dry out and feed again with smaller doses. Burnt tips don't heal, but they stop spreading.
How to avoid it
Start with less than the label dose, increase little by little watching how it responds, and measure EC if you can. A little bit of burnt tip in flowering means you are at the limit: don't go higher.
🎮 Practice it in UnderGrow
With the nutrient bar above 125 % the tips burn (above 100 % you already went too far). It is fixed with water › flush the soil, which lowers the nutrient bar by 50 %.
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