I purchased a bunch of extra packages of the powder, but I wanted to be sure so I also picked up some premixed reference solution as a final check. It is also important to note that the pH meters should be stored when not in use with a few drops of probe storage solution on the end of the sensor. I think it is a kcl solution usually. You could also use the premix reference solution on the probes if you want and save the kcl purchase. Pick up some distilled water for mixing the powders and rinsing the probe (don’t use distilled or RO water to water the plants unless you are trying for something specific - filtered isn’t necessary either).
It sounds complicated and expensive but it really isn’t, and as Peter said, so many nutrient problems can stem from pH instead of the actual nutrients. Some people get lucky and their tap water is close enough pH but most of us have to use a little pH down solution (or whatever you personally use to increase the acidity) to get in the correct zone. Check GWE for reference material but in general you don’t want the exact same pH for every watering, it should wander a little as different minerals do better at slightly different pH, as long as it is in the zone. The zone I believe for soil is 6-7 and coco is 5.5-6.5.
I haven’t used a soil tester so I can’t say for sure but I don’t think they are the greatest. Maybe someone else can comment on that one.
Re the solution you already have, I don’t think you can use it. I’m not sure what is in it but I assume it is not a calibration solution it is just for indicating pH using colour. If you knew the exact pH of the solution and it exactly matched the pH expected by your pH meter you could possibly use it but that isn’t practical and your digital pH meter will probably be a 2 or 3 point calibration anyways (which is why they come with 2 or 3 sachets of powder at different levels). Note that different sensors are often calibrated with different pH level calibration solutions so you should buy the meter first and determine what types of powders (pH level) you need to calibrate the device. I think mine is a 3 point calibration using pH 4.0, pH 6.86 and pH 9.18.
Shopping list:
-PH meter
-sachets of powder or premixed solution for calibration (at whatever levels requested by the meter)
-probe storage solution (reference solution or specific probe storage solution, both should work)
-distilled water
-it helps to have storage containers for the solutions made by the powders. You shouldn’t reuse the solutions but you don’t need to use the full amount at once, just mix enough in a separate container to submerse the probe end.(EDIT - to be more clear, mix the solution in the container you will store it in and pour out a little to use as necessary in a smaller container and then toss it when done). Seal the remaining tightly and preferably in glass containers
-optional: a premixed reference solution (any pH is fine as long as you know what it is) to double check your calibration
They say you should calibrate about once a week but you can adjust as needed if you find it shifting off the mark or not.
HTH
