MarcXLanswered grow question 4 years ago To me it seems like a copper deficiency as the tips and edges of leaves turn pale yellow.
This can happen due to root problems, wrong ph in soil or using dead water (distilled water, reverse osmosis water).
It is very unlikely that there is no copper available in your water or soil, so usually a copper deficiency in cannabis is caused by a pH problem at the roots that is restricting access to nutrients. Copper tends to get locked at certain pH levels, and is better absorbed by the plant in a slightly acidic root environment.
Copper deficiencies are more likely to appear when using heavily filtered or reverse osmisis water to feed plants since any copper has been removed, but ph is a much more common reason for copper deficiencies.
Copper deficiencies can show up when the plant is having root problems or if the plant is overwatered, even if the ph is right and the copper is there.
Flush your soil with clean, ph’d water that contains a regular dose of nutrients. This will remove any nutrient salts that may be affected the uptake of copper and help restore ph to the normal levels.
Watch to make sure that the problem starts to clear up within a couple of days. Old growth may not recover as copper is low-mobile, but new growth should be healthy.