The two most important factors in water and nutrient management are pH and conductivity, and a good understanding and command of these variables is essential for successful hydroponic gardening.
pH is the measure of acidity or alkalinity of an aqueous solution. If a solution is acidic then it has a pH in the range of 0 to 6.9. If a solution is alkaline then it has a pH in the range of 7.1 to 14. Pure water or deionized water is neutral at pH 7.0. The ideal pH for most hydroponic gardening applications is between 5.8 and 6.2, except for Rockwool cultivation, which likes a slightly lower pH of about 5.5.
If the pH of a solution is not within the correct range the plant will not have the ability to absorb some of the essential elements required for proper plant growth. All plants have a particular pH range, which will produce healthy growth, and this level will vary from plant to plant, but most plants prefer a slightly acidic growing environment (5.8 to 6.2), although most plants can survive in an environment with pH values between 5.0 and 7.0.
Plants grown in acidic environments can experience a variety of symptoms, including aluminum (Al), hydrogen (H), and/or manganese (Mn) toxicity, as well as nutrient deficiencies of calcium (Ca) and magnesium (Mg).
Conversely, in alkaline environments molybdenum (Mo) and macronutrients (except for phosphorus) availability increases, but phosphorus (P), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) and cobalt (Co) levels are reduced, and may adversely affect plant growth.
The best way to check pH levels is with a digital meter. All you have to do is dip the meter/electrode into the nutrient solution for a few moments and the pH value is shown on an LCD display. pH meters are fast and very accurate when properly calibrated. These meters need to be cared for properly or they will no longer function. The glass bulb electrode needs to be kept clean, and some are required to be kept wet at all times. pH meters also need to be checked and calibrated frequently to insure accuracy.
Although, most vegetables grown outdoors in soil do well in a range of soil pH levels, generally from slightly acidic (6) to neutral (7), hydroponics allows growers to pinpoint pH readings to create optimum conditions and maintain them. This not only leads to healthier, more productive plants but also avoids wasting the valuable nutrient solutions you feed them.
When grown hydroponically, most plants require slightly less pH levels than recommended for soil growing. Tomatoes do well in the ground outdoors with a high pH of 7. Hydroponic tomatoes are at their best in more acidic conditions, ideally with a pH of 6.0 to 6.5. Cabbage will do okay in alkaline soil with a pH as high as 7.5. Grown hydroponically, they’re at their best grown in neutral (7.0) to slightly acidic (6.5) solution.
There are several chemicals used by GRO Nutrients to adjust pH. The most popular for soil gardens are phosphoric acid (to lower pH) and potassium hydroxide (to raise pH). Both of these chemicals are relatively safe, although they can cause burns and should never come in contact with the eyes. Most hydroponic supply stores sell pH adjusters that are diluted to a level that is reasonably safe and easy to use. Concentrated adjusters can cause large pH changes and can make adjusting the pH very frustrating.
For hydroponic nutrient solutions, we recommend using phosphoric acid or Food grade citric acid to lower pH in your organic garden.
Always add the nutrients to the water before checking and adjusting the pH of your solution. The fertilizer will usually lower the pH of the water due to its chemical makeup. After adding GRO Nutrients® series of organic crop feeds and mixing the solution, check the pH using whatever method you chose. If the pH needs to be adjusted, add the appropriate adjuster. Use small amounts of pH adjuster until you get familiar with the process. Recheck the pH and repeat the above steps until the pH level is where you want it to be. Once you have done this a few times, you'll nail it the first try. Beyond all the facts and figures, this critical step is truly simple and easy.
The pH of the nutrient solution will have a tendency to go up as the plants use the nutrients. As a result, the pH needs to be checked periodically and adjusted if necessary. To start out, I suggest that you check pH on a daily basis. Each system will change pH at a different rate depending on a variety of factors. The type of growing medium used, the weather, the kind of plants and even the age of the plants all effect the pH variations.
With a ten-gallon reservoir feeding 10 medium size plants, you will need to check the strength (TDS or EC) and the pH of your solution at least once per day. People that know how to grow hydro usually use a larger reservoir. With a larger reservoir, the changes in the nutrient solution take a little more time. The larger reservoir acts as more of a buffer. A good general guideline to follow would be to use at least 3/4 gallon to one gallon of nutrient solution per plant. No matter what size reservoir you have, it is recommended that you check your nutrient solution at least once a day.
You should have a desired water level marked out somehow on your reservoir, and as your plants feed they will drop the level of the nutrient solution in the reservoir. Always begin by topping your nutrient reservoir up with plain water. It is a good idea to let any water that you use sit out overnight in an uncovered container. This lets the water de-Chlorinate, and also lets the water come to room temperature. Adding cold water can shock the roots, causing root damage below as well as damage and leaf drop above.
When checking your GRO Nutrients® solution, it is a good idea to check the nutrient solution strength first (as opposed to checking the pH first), because the addition of nutrients and supplements to the nutrient solution will usually change the pH of the nutrient solution a little. If the nutrient strength is low, add a little more of your base hydroponic nutrients. If the nutrient strength is a little high, add plain water.
After two weeks of using the same nutrient solution, it is time for a nutrient change. The plants may have been using some nutrients faster than others, and now you might be heading for a nutrient imbalance. Keep an extra nutrient reservoir full of plain water waiting for your next nutrient solution change. This ensures you will have de-Chlorinated, room temperature water that will not damage your plants' roots.
When adjusting pH, it is best to give your fresh GRO Nutrients® mixture several hours to stabilize before attempting to adjust it. You should also be aware that commonly available pH control products are very powerful, and a little bit too much can sacrifice your entire nutrient solution fast. For first timers, we suggest mixing up a single gallon of your GRO Nutrients® solution, letting it sit for a day, and then counting how many DROPS of pH adjustment (up or down) it takes to get it to a range of 6.0 to 6.5. You can then multiply your count by the volume of your reservoir as a baseline for rapid, full reservoir adjustments. Some nutrients may become unavailable to the plant if the solution pH drifts from an optimal reading, which for most plants is between 6.0 and 6.5. This condition is called "nutrient lockout”. pH can be tested with litmus paper and adjusted with an inexpensive pH control kit. Follow directions on your product’s packaging.
For optimal growth to take place, the nutrient concentration and pH must be consistently balanced over time to ensure that your plants have what they need, when they need it. In any circulating hydroponic system, with every pass the nutrient makes past the root system, an exchange is taking place. As a result, as time goes by, your GRO Nutrients® solution changes in concentration and that affects your plant's ability to uptake essential elements. Measure the Electrical Conductivity (EC) of your solution at least, every other day for optimal balance.