Few things in Hydroponics are as important as water. To get control of your water you’ll need an understanding of pH and TDS. This article will explain the tools and techniques used in testing, adjusting and controlling the levels of a nutrient solution.
One of the largest advantages to hydroponics is control, and one of the key factors to control is your water. Both the pH value and TDS (total dissolved solids) play a pivotal role in the health of your garden. If the water’s pH value is too low or too high the plants have trouble metabolizing a whole array of different nutrients. If your nutrient strength is too low it will likely cause deficiencies, too high and you get nutrient burn or lock out. This article will review the techniques and tools that will help you stay in control of your water.
pH stands for potential hydrogen, in chemistry terms it is the measure of the activity of the solvated hydrogen ion in a solution. In laymen’s terms it is the unit of measure indicating whether a solution is acidic, neutral or alkaline, and to what degree. The pH scale goes from 0 to 14. A pH value of 7 is neutral, any values below 7 are acidic, and any values above 7 are alkaline.
The pH scale is logarithmic and as a result, each whole pH value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. The same holds true for pH values above 7, each of which is ten times more alkaline than the next lower whole value. For example, pH 10 is ten times more alkaline than pH 9 and 100 times (10 times 10) more alkaline than pH 8.
Plants growing in soil typically like a pH value between 6.0 – 7.0. In hydroponics, plants like it slightly more acidic, and pH value between 5.5 – 6.5 is usually best. When outside of this range nutrients become less accessible for plants as shown in the graph below.
So now you understand the importance of properly balancing your water’s pH level, and the role it plays in the overall health of your garden. Now we should review the different ways to test and adjust pH.
Testing pH levels
In order to change or adjust the pH of a solution you must first have a way to accurately test it. You can use manual test kits or electronic meters to get your base level pH to determine if it needs adjustment, and if so, which way to adjust it, up or down.
Manual testing methods include Litmus papers or liquid test kits. Litmus papers are very inexpensive but can be quite hard to decipher. They are orange slips of paper that change color when dipped into a liquid solution. Each color represents a different pH value. The trouble is that the values we test at for gardening are often very close to the natural orange color of the litmus, making it difficult to pin point a result. Liquid test kits, on the other hand, will give much better results for only a slightly higher price. Both of these tests will only get you in the ball park of results, for more detailed testing you may want to look into a digital testing meter.
The vast majority of hobbyist level pH meters use a combined glass electrode for measuring the pH of a liquid solution. A combined glass electrode has an in-built reference electrode inside of a porous glass ball. For long probe life it is crucial to keep the probe hydrated with a storage solution to keep the pores on the glass electrode from drying out. A periodic use of pH electrode cleaning solution will also help in keeping sediment from clogging the pores of the glass electrode.
Frequent calibration is also a necessity with pH meters, as their readings can drift over time. Most meters will calibrate to a standard buffer solution of 7.0. Some meters will allow for a two point calibration calibrating to 7.0 and 4.0. A two point calibration is more accurate, as it will accommodate the fact that the “slope” may differ slightly from ideal.
Now that you can test your pH levels you can determine whether it needs to be adjusted. You want to be certain all your nutrients are added in as they themselves can alter the pH of the solution. pH adjustment should be your last step in making a nutrient solution. If you need to lower the pH of you water the best ingredient to use is phosphoric acid, the plants can just absorb it as another form of phosphorus. To raise the pH of a nutrient solution the best ingredient is potassium hydroxide that the plants can just take up as potassium.
Our in-store pH adjusters are made from phosphoric acid and potassium hydroxide. Unfortunately, since they are classified as an acid and base they have strict shipping regulations and we cannot offer them online. If you can’t find a local source for these adjusters you can use some household items in a pinch. Lemon Juice can work to lower the pH and baking soda can be to used to raise the pH.
TDS stand for total dissolved solids and refers to the measure of all substances contained in a liquid. It is the measurement used to determine nutrient strength. TDS in hydroponics has two different readings; Conductivity and Parts per Million (PPM). Conductivity is the more scientific of the two readings, it can be represented as Electro-Conductivity (EC), Conductivity Factor (CF) or Micro Siemens per square centimeter (MS/cm). PPM is not quite as accurate a representation of TDS but much more common within the United States. If you talk with a gardening friend or read information on a forum chances are the growers there will talk in PPM terms and not Conductivity.
PPM is directly calculated from Conductivity and there are two different scales: NaCl (1EC = 500ppm) and the 442 scale (1EC = 700ppm). Different meters offer different conversion factors and some offer a sliding scale or the option to change the scale to your choosing.
Testing your TDS
There are not many manual testing options for TDS and the ones we have seen use to large of a value range to be useful for hydroponics. Digital Meters are you best option for monitoring your nutrient strength.
All TDS meters are, in reality, conductivity meters, the PPM meter still measure conductivity but use a conversion formula to translate its reading to ppm. TDS meters work by applying a voltage between two or more electrodes. Positively charged ions will move toward the negatively charged electrode, and negatively charged ions will move toward the positively charged electrode. Because these ions are charged and moving, they constitute an electrical current. The meter then monitors how much current is passing between the electrodes as a gauge of how many ions are in solution.
TDS meters will only detect mobile charged ions. They will not detect any neutral (uncharged) compounds. Such compounds include sugar, alcohol, many organics (including many pesticides and their residues), and unionized forms of silica, ammonia, and carbon dioxide. These meters also do not detect macroscopic particulates, as those are too large to move in the electric fields applied. Bacteria and viruses also won’t be detected.
You can get the best of both worlds in one device with a combo meter. A combo meter will have the electrodes and components needed to test both the pH and TDS of a solution. Many people like this option for ease of use and less equipment to deal with.
Thank you for reading our article on “pH and TDS Explained”. If you have an questions or would like us to expand on some information in the article please post a response below. You could also contact us directly at 1-888-833-4769 (toll-free) or write to us at firstname.lastname@example.org. Now that you understand pH and TDS you ready to start growing hydroponically!