It is important to maintain the pH of nutrient solutions between 5.0 and 6.5. This helps ensure all nutrients are available for root up-take. It also minimizes the risk of plumbing blockages.
pH meters are useful for checking nutrient pH, however, they are very sensitive instruments and need to be well maintained.
When to Adjust pH
The working nutrient pH should be checked at the following times:
Nutrient reservoir with pH above 7: Calcium, sulfate, iron and other trace elements can precipitate in the reservoir and become unavailable for root uptake. FloraMax Flowering Enhancer helps “lock” pH below 6.5 and avoids needing a cal-mag.
1. When the nutrient solution is first made. 2. After the addition of top-up water or additives – especially if either are highly alkaline (Fig 13.1a & 13.1b). 3. In recirculating systems, pH should be checked on a daily basis because the uptake of water and nutrients causes pH to change.
How to Adjust pH
Step 1. Measure the pH: Use an electronic pH meter. Before measuring the pH, ensure that the nutrient is well stirred and that the sampling container is clean.
Fig 13.1a This is what can happen when an undiluted, high pH additive is added to the working nutrient solution. Fig 13.1b. Unless pH is quickly corrected to below 6.0-6.5, the precipitate will remain. A similar result can also be expected when other dosing techniques are not followed.FloraMax Flowering Enhancer is a 3-in-1 additive. It replaces PK additives, Cal-Mag-Iron additives and stabilizes pH below 6.5. @floramaxlab, @essence.farm.1
Step 2. Choose a Target pH: It is inconvenient and unnecessary to hold pH at a single point value. So, choose a target pH that provides both a safety margin and minimizes the amount of pH maintenance. For example, if your pH tends to continuously rise (the most common trend), then at each adjustment, reduce the pH to about 5.0 using pH Down. This will give you a much larger pH “safety” margin than, for example, 5.8. If pH tends to fall, at each adjustment increase the pH to about 6.0 using pH Up.
Step 3. Adjust the pH: Add a small amount (e.g. 1ml per 50 litres) of pH Down / pH Up. Then stir well and check pH. Repeat this process until the target pH is reached. When using pH Up, ensure to pre-dilute the dose at least 100-fold with water before adding to the nutrient.
How to Minimize pH Fluctuations (In Recirculating Systems)
1. Use a nutrient brand that is highly pH buffered, particularly when using very alkaline water.
2. Supply at least 10 litres (2.5 gal) of nutrient for each large plant. Failure to do this will magnify pH (and EC) fluctuations, especially during hot and dry weather when water uptake and evaporation are both excessive. To avoid excess water uptake and high evaporation rates, keep the air temperature below 30 deg C (86 deg F) and relative humidity above 50%.
pH Electrode Maintenance
Calibrating pH Meters
Fig 9.2 Always clean the electrode with distilled water after use. Then keep the electrode immersed (Fig 9.3) in a proper “storage” solution when not in use – the No.1 maintenance tip for prolonged electrode life !
It is essential to calibrate using at least two pH buffers. pH buffer 4.0 and 7.0 are ideal for nutrient solutions. Some manufacturers claim that their pH meters require calibration using only pH buffer 7.0. Professional practice however, stipulates using two buffers because this will confirm or otherwise that the correct calibration “slope” is being obtained i.e. that both the electrode and meter are ranging correctly.
Fig 9.4 Schematic layout of glass pH electrode. Loss of accuracy is invariably explained by different degrees of blockage of the ‘frit’ or ‘wick’ – often caused by dry storage, testing of harsh chemicals (e.g. pH Up or concentrated nutrient), or failure to rinse the electrode properly after use.
Dry Storage of pH Electrodes
This causes dehydration of the glass electrode and the precipitation of salts within the interstices of the frit itself (Fig 9.4). The consequences are slow response times and loss of accuracy and precision. To avoid these problems the electrode tip must be permanently stored (immersed) in a specially formulated storage solution (Fig 9.3). Note, pH buffers 7.0 or 4.0 and distilled water are NOT suitable for this.
pH Electrode Contamination
Unless the ‘frit’ and glass tip of a pH meter electrode is properly rinsed after use, it will invariably become contaminated with impurities (Fig 9.2). This causes similar symptoms to dry storage. Contamination may be so severe that re-calibration is not possible without prior cleaning or replacement. To prevent contamination, always avoid measuring harsh chemicals such as highly caustic solutions (e.g. pH Up and silica additives), or concentrated nutrient.
