Marijuana (Cannabis)

pH And Hydroponic Marijuana

pH is measured on a scale from 0.0 to 14.0. Pure water has a pH of 7.0 and is considered pH neutral. pH below 7.0 is considered to be acidic and pH higher than 7.0 is considered to be alkaline.

A substance that decreases pH (pH-down) is called an acid while a substance that increases pH (pH-up) is called a base. A substance that helps resist pH changes when an acid or base is added, is called a buffer.

A pH difference of 1.0 is equal to a ten times increase or decrease in pH. That is, a nutrient solution with a pH of 6.0 is ten times more acidic than a nutrient solution with a pH of 7.0. A pH difference of 2.0 is equal to a hundred times increase or decrease in pH.

It is very important to keep the pH level within certain limits when growing soil or hydroponic marijuana. Even first time marijuana growers need to monitor the pH of their soil or nutrient solution and keep it within optimum levels.

The pH level of your hydroponic nutrient solution or soil will determine how well your plants are able to absorb nutrients. If the pH level is out of the proper range, the growth rate of the plants will slow down or stop.

Temperature, nutrient, and pH problems are the top three things that cause a crop failure when growing hydroponic marijuana. By monitoring and keeping them within optimal ranges you will maximize the chances of a successful crop.

Optimal pH
Measuring pH
Adjusting pH
pH Controller
List Of Materials

Optimal pH For Hydroponic Marijuana

When growing hydroponic marijuana the optimal pH for the nutrient solution is between 5.8 to 6.2. Once the pH goes out of the optimal range, growth will slow or stop.

It is better for the pH to be under 5.8 than it is to be over 6.2. As the pH rises above 6.2, plant growth slows down more than it would when it is under 5.8.

If the pH is maintained above 6.2 for extended periods of time, it will eventually cause the plant to stop growing until the pH is brought back into optimal range.

Never let the the pH get out of the range of between 5.3 and 6.5. If a plant is supplied with nutrient solution with pH outside the 5.3 to 6.5 range for any amount of time, it can permanently damage or kill it.

There were times when the pH of the authors nutrient solution had been at dangerous levels for short periods of time, because the pH was measured only once per day. Plant growth had stopped, but the plants were not damaged or killed.

Once the pH was brought back to optimal levels, the plants resumed growing in a day or two. In order to reduce or eliminate the chance of this happening again, pH measurements are now performed more often.

Measure the pH after you add nutrient to the water that will fill the reservoir, mix well first because the nutrients will change the pH level of the water. Adding nutrients should lower the pH of water.

Check the pH everyday, or several times a day if necessary, and make sure it is within the proper range. Depending on the marijuana strain being grown, some growers report good results with pH lower than 5.8.

However, you should try to maintain 5.8 to 6.2 pH readings for your first few crops. When you are confident in your ability to raise a crop, you can try experimenting with pH.

Measuring pH Of Hydroponic Nutrient Solution

When growing cannabis, the two most common methods of measuring the pH level of the hydroponic nutrient solution are pH test kits and pH meters.

A pH test kit has a container in which nutrient solution is placed. A few drops of test indicator are added to the nutrient solution in the container and mixed together.

The resulting color of the liquid in the container is compared with the color on a color comparison chart, that comes with the test kit, to obtain a pH level measurement.

Oakton EcoTestr pH 2

A pH Meter measures the pH of water and other liquids, hydroponic nutrient solution, hydroponic media, etcetera.

Meters are long lasting, and will give more accurate results than a test kit, but they are more expensive.

A pH test kit is cheap and provides adequate results. If your budget allows for it, a good pH meter is preferred.

Adjusting pH Of Hydroponic Nutrient Solution

pH-up and pH-down are used to adjust the pH level of hydroponic nutrient solution and hydroponic media when the pH is out of range.

pH-up, also called pH increase, is added to raise the pH level. pH-down, also called pH decrease, is added to reduce the pH level.

For hydroponic applications, nitric, phosphoric or citric acids (even vinegar) can be used to lower pH. While potassium hydroxide can be used to raise pH.

If you understand what you are doing, you can use these various chemicals instead of buying pH-up and pH-down, contributed by james and jorge.

However, if you aren't sure of the correct amount of acid or base that is needed to adjust the pH to optimum values, it is best to buy a product specifically made for hydroponics or aquariums.

Don't try to adjust your nutrient solution pH by more than by about 1.0 per day. Always make drastic changes in small increments over a two day period.

pH Controller

A pH Controller is designed to automate the adjustment of pH levels of liquids like hydroponic nutrient solution. The controller section monitors the pH level with a probe.

When the pH goes out of the level you choose, the controller sends a signal to pumps that add either pH-up or pH-down to the nutrient solution.

Some pH controllers allow you to set a high level and a low level. When the pH level goes out of range, the controller will either turn on a pH-up or pH-down pump to adjust the pH.

Other pH controllers only allow you to choose either a high level setting, or low level setting, that will activate the pump.

When the high level setting is selected and the pH rises to a level above what you select, the controller will turn on a pump that releases pH-down into the nutrient solution.

When the low level setting is selected and the pH falls to a level below what you select, the controller will turn on a pump that releases pH-up into the nutrient solution.

List Of Materials
pH meter
pH test kit
pH controller
pH-up and pH-down

*** pH meter A pH meter is a very good way of measuring the pH of hydroponic nutrient solution. However, the price may make meters out of reach for growers on a budget.

In general, pH meters that cost under about $50-$60 US are less accurate and slow. They should be avoided unless quick and accurate measurements are not important.

Besides the pH meter itself, you also need to purchase pH calibration solution to calibrate the meter with, and may require electrode storage solution to extend electrode life/minimize how frequently you have to calibrate the meter.

Calibrating a pH meter correctly is especially important. This is because all measurements will be wrong if the meter is mis-calibrated.

pH calibration solution is commonly sold at pH levels of 4, 7, 10. For hydroponic marijuana you can get by calibrating at just 4 and 7.

You can calibrate your meter at 4, 7, 10 but it is not necessary. If the pH is not within the 4-7 range, hydroponic marijuana plants will probably be dead.

My Oakton meter has worked since 2012 without any problems. It's easy to calibrate, accurate, fast, waterproof, and relatively inexpensive when compared to other accurate pH meters.

Measurements are taken several times a day and it gets calibrated every 1-2 weeks. pH electrode storage solution is placed in the cap to extend its life and maintain accurate readings. Batteries have had to be replaced about once a year.

pH 7 calibration solution was once used to keep the probe wet. A week later the meter started giving error messages when calibration was preformed. When pH probe storage solution was employed instead, there were no more calibration problems.

For accurate hydroponic measurements always follow the manufactures instructions for calibrating, cleaning, storing, and working with a pH meter.

Be sure to get a pH meter intended for liquids if you have a hydroponic garden. There are some pH meters that are strictly to measure the pH of soil.

*** pH Test Kit A pH test kit is an inexpensive way to measure pH for hydroponic growers on a budget. They are not as accurate as pH meters but they will do the job.

Look for a pH test kit for measuring liquids, that can at a minimum measure pH between 5.0 and 7.0. A pH test kit for hydroponic applications is recommend, but aquarium test kits may work too.

This link goes to a pH test kit that covers a pH range of 4.0 to 8.5, which is good for measuring hydroponic nutrient solution when growing hydroponic marijuana.

It includes sampling tube, test indicator, and color comparison chart. Additional quantities of the test indicator can be purchased separately.

A pH test kit for liquids works by putting a small amount of nutrient solution in a container then adding a few drops of pH test indicator liquid and mixing them together.

The combined mixture will turn color. This color is then matched with the color on a pH chart, included with the test kit, to determine the pH level of the nutrient solution.

A pH control kit like this contains a pH test kit to measure the pH of liquids like water or hydroponic nutrient solution. In addition it includes pH-up and pH-down to raise or lower the pH.

First time hydroponic marijuana growers on a budget should consider getting a pH control kit. It contains everything you need to measure and adjust the pH of hydroponic nutrient solution.

*** pH Controller A pH controller is very handy and will allow you to easily maintain optimum pH levels automatically, without having to be there to physically do it yourself. The drawback to pH controllers is the price.

*** pH-up and pH-down To raise or lower pH, pH-up and pH down can be used. For hydroponic marijuana or other plants, look for a product specifically made for hydroponics or aquariums.


1 --- pH is harder to maintain with deep water culture and recirculating hydroponic systems, than it is with drain to waste systems.

With recirculating systems the nutrient solution is supplied to the roots of plants, usually with a pump, then the nutrient solution flows back into the nutrient reservoir.

When nutrient solution is supplied to the plant roots, the roots will usually absorb a certain amount of nutrient, which causes the pH level to rise.

Then the nutrient will flow back into the reservoir, and it will raise the pH level of the rest of the nutrient solution contained in the reservoir.

With drain to waste systems, the nutrient solution is supplied from the reservoir to the plant roots, then it is discarded. So it has no effect on the pH of the nutrient solution in the reservoir.

Checking the pH of a drain to waste system can be done less often than with deep water culture and recirculating hydroponic systems.

2 --- With a recirculating hydroponic system, you may observe that after you change the nutrients, the pH goes up. Then a few days after the nutrient change, you may observe the pH starting to go down.

When you see this kind of pH rise after changing nutrients, followed by the pH falling a few days later, it is probably because you are not changing the nutrient solution often enough.

Start changing the nutrient solution more frequently, so the nutrient solution is changed before the pH starts to decline, or just when it starts to decline. Your plants will grow faster and be healthier.

3 --- With a deep water culture or a recirculating hydroponic system, a reservoir that holds a larger amount of hydroponic nutrient solution will make it easier to maintain pH levels.

If a given group of plants were moved from a recirculating hydroponic system with a 50 gallon reservoir to a system with a 20 gallon reservoir, and all other factors (like light, temp, etcetera) remained the same, the pH would change more rapidly in the 20 gallon reservoir.

With a deep water culture or a recirculating hydroponic system, to help make keeping the pH of the nutrient solution within range easier, always get a reservoir that is the maximum size that is practical.

Related Books

Grow Great Marijuana
Very good choice for simple and accurate instructions about growing hydroponic marijuana. Does not cover advanced techniques, but if you have no experience, this is the first book to look at.
Grow Great Marijuana

The Cannabis Encyclopedia
Easy to read with comprehensive focus on growing and consuming for medical and recreational purposes. This will be of interest to growers, patients, caregivers, consumers, or anyone interested in consuming, growing, or producing cannabis products.

Over 2,000 color images on 596 pages. Loaded with recent information covering all aspects of marijuana. The grow section explains hydroponics and soil growing, growing indoors, outdoors, and in greenhouses.
The Cannabis Encyclopedia