What Is pH And How Do I Test pH?

What is pH?

PH is the measurement of acid or base in a solution.  The pH scale is a logarithmic from 1 to 14 with 7 being neutral.  Scores from 1 to 6.9 are considered acidic and scores from 7.1 to 14 are considered to be base (or alkaline).  Remember logarithmic scales increase by a factor of 10 for each number away from the start.  So moving from 7.0 to 6.0 means the solution is 10 times more acidic and moving from 6.0 to 5.0 is 100 times more acidic.  This is important to remember when adjusting levels.  An example of a neutral pH solution is pure water.  If you tested your bottled water in the refrigerator it should score a 7.

Why is pH important in hydroponics?

Maintaining a proper pH level ensures your plants can absorb the essential nutrients for optimal growth.  One of the most pH sensitive and impactful nutrients on your plants is iron.  Iron precipitates out (leaves the water and sticks to the sides of your reservoir) above 7.3. While below 6.0, iron becomes so available to your plant it could be toxic. The ideal pH range varies slightly by plant but a good rule of thumb that works for the majority of plants is maintaining a range of 6.0 to 7.0.

How do you test pH levels?

Testing pH levels of your hydroponic system is very easy with some basic equipment.  Today you have 3 options to test your pH:

Litmus paper:  Provides rapid readings as you just dip a pretreated testing strip into the solution.  However, this is not recommended for hydroponics as they only provide very crude results to the nearest whole number and can be difficult to even interrupt the color charts. Remember the scale is logarithmic so the difference between 6.0 and 6.5 is 50 times more acidity!

Liquid pH testing kits: These are most popular for the new hydroponic hobbyist as they are better then litmus paper but a cheaper alternative to pH meters.  Testing with kits should keep you from killing your plants but you may not achieve maximum yields without a more accurate pH meter.  Using a liquid testing kit is easy.  Most all kits use these basic steps.

  • Fill test vial ½ way with your nutrient solution
  • Add a few drops of pH test indicator
  • Tap the side of the vial to mix
  • Match the color to the color chart provided in the kit

pH Meters:  Meters use a probe and a microprocessor to achieve fast and very accurate results.  They are simple and easy to use but have 3 downsides: cost, the probes must be replaced approximately once a year and you must take special care to calibrate and store the equipment between uses.

How often and when do you test your solution’s pH?

You should test your solution daily when you first set it up or make any significant changes.  Once your system settles into a ‘steady state’ you can start testing every few days.  You should also add your fertilizer to your nutrient solution prior to testing as the fertilizer typically lowers the pH of your water.

How do you adjust pH levels?

Once you know your pH levels you will likely need to adjust them either higher or lower.  The most common way to decrease the pH is to add phosphoric acid and the most common way to increase pH is to add potassium hydroxide.  If you are a hobbyist or just starting out, you should seek an adjustment kit that uses diluted phosphoric acid and potassium hydroxide.  The concentrated forms can cause huge pH swings in small hydroponic systems.

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