Fighting Marijuana Plant Foliage Death
Leaf death on your marijuana plants can come as a surprise, if you see discoloration (yellow, brown, gray, sometimes even red), and damaged edges, leaf drop is not far away. The key is to diagnose the problem as quickly as you can so that you can fix the problem when it attacks your marijuana plant, to continue towards a healthy harvest. There are three possible causes; the imbalance of the PH, too little or too little watering or a nutritional imbalance; to do so, a diagnosis is required and it begins with checking the level of the PH
PH imbalance
The pH is more important than one would like to admit, this balance manages the consumption of nutrients and water, and therefore a bad pH has a strong toxic effect on the plants, in terms of nutrients, induced by imbalances and deficiencies. In general, it is always a good idea to check the pH levels at the first symptoms on your marijuana plant.
The plant itself has a pH identity, some plants being more acidic and others more alkaline, the water of different regions has a pH identity determined by a series of environmental factors, the soil, your soil also has a pH identity . The pH level is simply a measure of all this, in alkaline or acidic terms, the measure is between 0 to 14

The highest level is the most alkaline; the lower, the more acidic. Ideally, the water you feed your marijuana plants with should be a perfectly balanced level of 7. The soil should also have a balanced pH level. Measuring the pH level is quick and simple, and should be done with relative frequency.

If your results are too high or too low, you can adjust it accordingly with natural supplements or a store-bought product like “pH Up / Down”. If you need to lower the pH level, you can also just 'whip' your water to increase the oxygen level and hence the pH level as well ... Keep in mind that the ideal pH for the Nutrient uptake is between 6 and 7 for soil crops and between 5.5 / 6.5 for hydroponic systems.
Watering problems
Once you have restored the pH level and the effect persists, it is possible that the water will cause the death of the foliage and it is necessary to evaluate the watering ... It is important to take into account the environment of crop you are using, if watering is the problem then you have a concern with drainage or the amount of watering.

To determine if the watering is responsible, you make sure that about 20% of the water you give your plant is drained. Once you've drained 20% (of all), you need to let the soil settle until it's dry again - then water it with the same technique. To determine if the soil is dry enough for another watering, put your finger in the ground, and gauge the humidity, if the soil is totally dry, you can water again.

Hydroponics will not have excessive flow problems, but the culture environment can be "drowned" if oxygen is lacking ... In the case of hydroponics, place an aquarium air stone and make sure that the oxygen diffuses well in your culture medium.

Obviously the problem with poor watering is excess water, poor drainage, bad temperature which leads to rotting of the roots. In this case the roots will be brown and smelly, use a product like Aqua-shield to banish the rot that plagues the roots.
Thermal stress
Heat stress occurs when your plant is too close to the light source. The solution to this problem is simply to reduce the heat; outside we will give more water and we will find a system to create shade (canis), indoors it is a little more delicate.

For an indoor culture, you will need to evacuate the hot air using an extractor (exhaust fan) or accommodate fans. The easiest solution is to install a small fan on top of the plants.
Nutritional imbalances
Once you've established the pH levels and adjusted your watering, and leaf death persists, you can assume a nutrient imbalance, or more accurately, a nutrient imbalance. Nutrient combustion occurs when too much hydroponic solution is applied, the roots store more nutrients than they should ... This is the case for too rich soil such as compost, manure or any excess nutrients in the soil . In a hydroponic system, all you need to do is reduce the nutrient supply in your nutrient solution by adding clear water (adjusted pH); or to mix a more dilute solution. For a hand sprinkler system, you need to drain it with a large amount of water.

The old leaves may not be regenerated, but the news will behave better. When the plants regain vigor, consider also adding algae extracts to replace the lost nutrients. Some growers believe that it can also prevent heat stress.

Whether it is a deficiency, or the toxicity (or its excess) of a certain nutrient; you will need to dig deeper into your symptom research to determine which type of nutrient may be missing or which may be causing toxicity to your plant.