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Test Equipment FAQ

How do I calibrate my pH meter?


All pH meters need to be calibrated on a regular basis; as time passes by and with frequent use your pH meter it will lose calibration. You will also find that as the batteries get older your meter will loose calibration. Keeping your meter calibrated will help keep your plants in good health and at optimal growth.

Your method of calibration will depend on what type of meter you own. pH meters require that you calibrate the meter with two pH solutions, pH 7 (neutral) and pH 4 (acidic). If you use your pH meter every day it is advisable to calibrate your meter once a week. To calibrate your meter you will need three clean glass/plastic containers that can hold sufficient solution to immerse the pH probe. One container will hold water for rinsing the probe, another container for the pH 7 solution and the last container for the pH 4 solution. Before you calibrate your meter do a visual inspection of the meter. Check for cracks on the meter, algae or salt deposits on the probe or any matter that shouldn't be on the probe. If there is algae or salt deposits on the probe clean it with a moist cotton swab. Once this has been done you are ready to calibrate your pH meter.

How do I calibrate my TDS meter?

Basically what these meters do is measure the flow of electrical current between the two metal posts in the probe. The more salts/nutrients that are in the water, the higher the reading. A TDS/PPM/EC meter needs to be regularly calibrated. If the meter is used daily then the meter should be calibrated weekly. If the meter is used less than daily then it should be calibrated once every two to three weeks. You don’t want to leave it much longer than this because as the battery life decreases the meter looses its calibration. Every time you replace the batteries on your meter or even take the batteries out of your meter you should recalibrate. You should check the meter regularly for cracks and salt deposits on the electrode. Always allow the calibration solution to warm up to room temperature, especially if the solution is stored in the refrigerator.

What is pH, why do I have to worry about it, and how do I maintain it?

pH stands for “Potential of Hydrogen” and is the symbol for the hydrogen ion (H+) in liquids. pH has a range from 0 (acidic) – 7 (neutral) – 14 (alkaline). For hydroponics, we are aiming for a pH between 5.5 to 6.2 (slightly acidic); this is suitable for most hydroponic crops. Ensuring that the pH remains within this range will help maintain good plant health. Keeping the pH in this range ensures that nutrients are readily available to the plant. Once the grower goes above or below this optimal range certain nutrients start becoming unavailable to the plant (e.g. – iron deficiencies will appear at a pH of 6.5 and above). pH is maintained by adding either pH Up or pH Down (see “What is pH Up and Down?”).

What is pH Up and Down?
pH Up is potassium hydroxide and pH Down is phosphoric acid (commercial growers will sometimes also use Nitric acid and Sulfuric acid). Customers who use tap water will normally need to use pH down to balance the pH of their nutrient solution. Tap water tends to have a lot of carbonates which tends to buffer tap water at a higher pH. Customers who use RO water will need to use pH Up as the reverse osmosis strips the tap water of all the carbonates, thus leaving the water with no buffering ability. The nutrients the growers use to feed their plants is acidic, and once the grower has applied all the required nutrients and enhancers the reservoir pH can be below 5. This is too low for plants; thus pH Up needs to be used in order to raise the pH to 6. Customers using both pH Up and Down should take care when using these products as both are very concentrated. Only small amounts should be used at a time until the customer becomes familiar with the products.
What is TDS, PPM and EC, why do I have to worry about it, and how do I maintain it?

TDS, PPM and EC represent the amount of nutrient salts that are dissolved in water. Pure water will have a TDS, PPM or EC reading of 0. Distilled water will have a reading just above 0 (e.g. 4ppm or 6µS) and RO water about 5 - 30ppm. Total Dissolved Solids is measured as PPM (Parts per Million). Electrical Conductivity (EC) is measured in milliSiemens (mS) or microSiemens (µS), depending on the type of meter. To find out why and how you need to maintain these levels, see “What ppm should be given to plants”.

TDS - Total Dissolved Solids

PPM - Parts Per Million

EC - Electrical Conductivity

What PPM should be given to plants?

Different plants require different strengths of nutrient solution, e.g. lettuce cannot be fed the same nutrient strength as tomatoes.

Click here for a general guide and can be used for most plants

Plants should never be subjected to a sudden increase of more than 200ppm in the nutrient solution from one watering to the next. The transition from one growth stage to the next should take place over a few days. Clones and seedling should always be fed a low ppm (nutrient strength) in the beginning. Over the next few days the ppm’s can be increased up to 800ppm. Clones that are subjected to a ppm strength of 800ppm straight after transplanting will go into stress and shock. Clones and seedlings should always be kept for at least one week in the vegetative stage before attempting to put the plants into the stress of flowering. This gives the plant some time to acclimate to its new environment and also gives the grower a chance to gradually increase the nutrient strength.

How do I properly store my meters?
pH Meter

Always remember to keep the pH probe moist when not in use. It is best to use pH Electrode Storage Solution; if you have run out of storage solution you can use pH 4 solution as an alternative. For the Hanna HI98129 black combo meter, place storage solution in the well of the cap that the pH electrode (not the TDS electrode) rests in. It is not advisable to store the EC/TDS/CF/PPM probe in any storage solution.

TDS Meter

The best way to store your TDS meter is to keep it clean and dry. TDS meters do not require any storage solutions. DO NOT store the TDS meter in distilled water.

For long term storage, make sure that the batteries are removed from the meter as leaking batteries will corrode the circuit board rendering the meter useless. None of our meters’ warranty covers leaking battery damage. For long term storage of the pH meter it is best if the probe is stored in sufficient storage solution; if the solution evaporates then the pH probe will dry out.

How long should my meters last?
The warranty on pH and TDS Meters is one year. The warranty on pH probes is 6 months. If the pH probe is looked after as directed it can last one to two years. TDS probes can last longer than pH. It is quite common for TDS meters to last a number of years with good care.
How do I use a digital meter to test soil pH?

1:2 Dilution Method

1. Mix 3 oz. of soil with 6 oz. of distilled water

2. Let mixture stand for 15 to 20 minutes

3. Filter liquid into clean cup

4. Take reading

How often do I need to calibrate my pH/TDS meters?

All pH and TDS meters need to be continuously calibrated; as time passes by and the more you use your pH meter, it will continually lose calibration. As the meter’s batteries get older it will also lose its calibration. Keeping the meter calibrated will help keep your plants in good health and at optimal growth. All pH and TDS meters must be recalibrated every time you change the batteries. It is good practice to calibrate your meters once a week, especially if the meters are being used daily.



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