If I use a Nutrient Meter (CF Truncheon) do I still need a pH meter?
That’s a great question. The answer is No – or Yes if you are not using town water, or if you are recirculating for a while.
pH meters tell you how “available” the nutrients are to the plant. Its important only if the pH is wrong. Most town water supplies are around 7-8pH out of the tap. This is a world health organisation standard, and stops the copper dissolving out of your pipes and giving your basins and bathtubs a blue ring from the copper.
What that means is that the pH of the nutrient in the bottle can be made to mix to the correct pH. If the tap water is 7.5 and the nutrients are designed to pull the pH down by around 1.0pH, that will bring the pH to around 6.5 which is nearly ideal. This is also part of the reason that pH tends to rise in most recirculating systems.
If the pH was below 6.0 many major elements become unavailable. So if the pH is below 6.0, then you must do something about it. Add only Phosphoric Acid (or Nitric if you’re keen) and dilute it. If the acid goes in too strong, the nutrient can knock out the nutrients in the solution. If you do it too strong, you will see a cloudy trail where you have added it. This is the nutrients dropping out of solubility and becoming a powder.
If you need pH Raise, its a little unusual, often from too much pH down, or light levels being too low. Add Potassium Hydroxide in a diluted from and avoid cloudy trails where you add it. Dilute more to avoid knocking out your nutrients.
If the pH is above 7.0, some minor elements become unavailable. So if the pH is above 7.0 you don’t need to panic. The plants are not at their optimum, and adjustment is a good idea to maximise performance.
pH tends to be wrong when the nutrients are depleted from recirculation, or if someone is using rainwater, bore water or anything other than town supplies. So if the pH starts right, we usually find the nutrients can circulate from 7-10 days and then get dumped. Some growers feel that by using the nutrient tester and pH adjustment means you can circulate forever. That’s not true. The nutrients become imbalanced, too much of some minerals, too little of others. Adding nutrient doesn’t re-balance it enough, it just keeps getting worse.
If you are only hand watering a medium, the pH may change in the media itself, so flush it every 1-4 weeks. The more often, the better balance.
As for the nutrient tester, this meter actually tells you something about the plant, and gives you control of the plants height, branching, growth rates, and is a great tool you should use. For my guide on nutrient control, see http://www.hydrocentre.com.au/phcf/ and our growing guides at http://hydrocentre.com.au/growing-info/
Perhaps a $10 pH test liquid kit can help you check the pH to see its alright – without having to test all the time, or spend a lot on pH equipment. If its all fine, you know its ok.
I hope this helps.