Essential Tools for Hydroponics

phmeterThere are two tools essential for hydroponics that most people aren’t familiar with – the Total Dissolved Solids (TDS) meter and the pH meter.  Knowing how to use these tools is important to the success of your hydroponic garden.

TDS Meters

TDS meters measure the combined inorganic and organic substances dissolved in a liquid – in our case, water.  While lab-grade TDS measuring equipment is very expensive and difficult to use, there are a number of inexpensive TDS meters designed to allow rapid, accurate measurements.

The TDS meters used by hydroponic gardeners measure using conductivity.  Pure water is a very poor electrical conductor, but when other materials are dissolved in it the conductivity improves.  The TDS meter measures the conductivity and converts it into a very close approximation of the total dissolved solids in the water expressed in parts per million.

When you are mixing your nutrient solutions, the instructions will usually express concentrations in parts per million.  When starting with a new nutrient, you can add a little bit to your water, stir well until dissolved, and measure the TDS.  Keep adding nutrients until you reach your target TDS.

Your TDS meter will last a long time as long as you remember to rinse off the electrodes after use.

pH Meters

pH meters are used to measure the acidity of your nutrient solution.  Plants need their water/nutrient solution to be in a fairly narrow pH range.  To high or too low and the plans will not be able to absorb the nutrients.  pH is measured on a scale from 0 (highly acidic) to 14 (highly basic).  Pure water has a pH of 7, while lemon juice has a pH of about 2 and bleach has a pH of roughly 13.5.

Different plants like different pH ranges, which can range from pH 5 to pH 7 depending on what you’re growing.  Here are some common plants and the pH ranges they like:

Chives: 6.0 – 6.5

Tomatoes: 5.5 – 6.5
Cucumbers: 5.8 – 6.0
Peas: 6.0 – 6.8
Lettuce: 6.0 – 6.5

Once you have mixed your nutrient solution you will need to measure the pH and, if necessary, adjust it to be in the range required.  Digital pH meters are easy to use and give fast, accurate measurements, but they do need to be cared for and calibrated regularly.

To use a pH meter you simply place the electrode in your nutrient solution for a few moments and the pH value is displayed on the LCD screen of the meter.  After use, it is important to properly store the pH meter.  The electrode just be kept clean and with most meters must be kept wet at all times.  There are special electrode storage solutions that are recommended for storing your pH meter.

pH is temperature dependent, so look for a pH meter with automatic temperature compensation (ATC).  Without ATC, the pH reading of your nutrient solution will be different if measured at different temperatures, making it difficult to get an accurate, repeatable measurement.

Your pH meter will need to be calibrated, as they can drift.  Be sure to purchase some calibration solutions when purchasing your pH meter and follow the manufacturer’s instructions for checking and calibrating your meter.

To adjust the pH of your nutrient solution you can phosphoric acide to lower the pH and potassium hydroxide to raise it. While these chemicals are relatively safe, they can be dangerous in high concentrations. Most people prefer purchase the easy-to-use pH adjusters available from a variety of sources, such as General Hydroponic’s pH Up and pH Down products.

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