Marijuana plants have voracious appetites and devour nutrients. During the vegetative period they generally have a great need for nitrogen (N) and during flowering they often need extra phosphorous (P). The other key nutrient is potassium (K), which is required at both stages of growth. Feeding solutions deliver the goodness your plants need in an effective and convenient way. Here's how to make one.
Fill a container with about 100L of lukewarm water. Measure the EC value of the water itself. Measure and stir in the fertilizer(s) of your choice. Depending on the EC value for which you are aiming, you will need anything between 200cc and 400cc of good-quality commercial fertilizer. As a rough rule of thumb, for young plants you should be looking at an EC value of 1.5 and for mature ones an EC value of 2.5 is reasonable. The EC value should be increased in increments of 0.1 every third or fourth day and the plants monitored for any signs of discolouration. If discolouration occurs, the EC value should be dropped back for another 3 to 4 days. If discolouration occurs again then the EC value is as high as it can go for this crop. The EC value is measured with an EC meter, also known as a TDS meter. If it's too low then more fertilizer needs to be added. If it's too high then more water needs to be added.
The other key value is the pH level. For hydrophonics this should be in the region of 5.5. to 6.5 and for soil 6 to 7. If the pH value is lower than this, the mixture is too acidic and should be balanced with potassium hydroxide. If it is higher than this, then the mixture is too alkaline and should be balanced with nitric acid or phosphoric acid. Again, the pH value can be measured with a digital metre.
Finally you want to serve your plant its food at the right temperature, i.e. around 22º Celsius. Aquarium heaters can work very nicely for this purpose and aquarium pumps can be used to keep the water circulating and therefore stop it becoming stagnant and potentially filling up with harmful germs.