from the
Marijuana Grower's Handbook - part 15 of 33
"pH and Water"
hxxp://www.lycaeum.org/~sky/data/mjgrowers.html
The pH is the measure of acid-alkalinity balance of a solution. It is measured on a scale of 0-14, with 0 being the most acid, 7 being neutral, and 14 being most alkaline. [pH:In case you're wondering, I'm a total 0!] Most nutrients the plants use are soluble only in a limited range of acidity, between about 6 to about 7.5, neutral. Should the water become too acidic or alkaline, the nutrients dissolved in the water become too acidic or alkaline, the nutrients dissolved in the water precipitate and become unavailable to the plants. When the nutrients are locked up, plant growth is slowed. Typically, a plant growing in an environment with a low pH will be very small, often growing only a few inches in several months. Plants growing in a high pH environment will look pale and sickly and also have stunted growth. All water has a pH which can be measured using aquarium or garden pH chemical reagent test kits or a pH meter. All of these items are available at local stores and are easy to use. Water is pH-adjusted after nutrients are added, since nutrients affect the pH. Once the water is tested it should be adjusted if it does not fall within the pH range of 6 to 7. Ideally the range should be about 6.2-6.8. Hydroponic supply companies sell measured adjusters which are very convenient and highly recommended. The water-nutrient solution can be adjusted using common household chemicals. Water which is too acidic can be neutralized using bicarbonate of soda, wood ash, or by using a solution of lime in the medium.
Water which is too alkaline can be adjusted using nitric acid, sulfuric acid, citric acid (Vitamin C) or vinegar. The water is adjusted using small increments of chemicals. Once a standard measure of how much chemical is needed to adjust the water, the process becomes fast and easy to do. Plants affect the pH of the water solution as they remove various nutrients which they use. Microbes growing in the medium also change the pH. For this reason growers check and adjust the pH periodically, about once every two weeks.
The pH of water out of the tap may change with the season so it is a good idea to test it periodically.
Some gardeners let tap water sit for a day so that the chlorine evaporates. They believe that chlorine is harmful to plants. The pH of the planting medium affects the pH of the liquid in solution. Medium should be adjusted so that it tests between 6.2-6.8. This is done before the containers are filled so that the medium could be adjusted in bulk. Approximately 1-2 lbs. of dolomitic limestone raises the pH of 100 gallons (4.5-9 grams per gallon) of soil 1 point. Gypsum can be used to lower the pH of soil or medium. Both limestone and gypmsum have limited solubility.
There are many forms of limestone which have various effectiveness depending on their chemistry. Each has a rating on the package.
This is what I've been doing, so far so good.
cheers
