In case anyone has the same question, I spoke with Luke from Apera Instruments. He advised that for low acidic testing with the 1.68pH buffer, the calibration sequence should be: start with 7.00pH, followed by 1.68pH, and finish with 10.01pH, effectively replacing the 4.00pH buffer with the 1.68pH buffer. Be aware that if you calibrate for low acidity and you do not recalibrate the pH meter and then test something that needs to be within the 4.5-5.5pH range, the results may be slightly inaccurate. Hope this helps!

pure water refers to distilled water/RO water/deionized water

When the reading is greater than 2000 µS, the unit will be automatically converted to mS. 1 mS = 1000µS. For example, if the reading is 2500µS, the display will be 2.5 mS on the screen.

1. Water droplets are added before the new product leaves factory just to keep a minimally required humid atmosphere for the probe. In terms of water type, using tap water or drinking water is good.

2. Soaking in 3M KCl for long term storage is the best practice for the pH probe. It will ensure the probe to have its optimal performance. The reason we didn't add KCl in the probe cap when the meter leaves factory is because the solution could leak out during transportation and people might think this is not in new condition. Storing with a few drops of water can prevent the pH probe from being dried out, but it's not going to maintain the probe at its best condition.

3. Yes you are right. Never soak the probe in pure water because it can damage the probe's reference system and cause measurement inaccuracy in the long term. For probe soaking, please use 3M KCl.

@@aperainst Thank you for the responses. Since posting my original comment, I have researched the topic myself. So for the sake of further clarifying the issues around storage, and the use of various types of water, could you please confirm whether the following is correct? From my research, I've found out that the probe is comprised of layers of semi permiable glass, between which is an electrolyte solution. The exact composition of this solution can vary from manufacturer to manufacturer. When you store the probe in tap water that has a different balance and composition of electrolytes, or worse yet, distilled or de-ionized water that is very low / free of electrolytes, the solution inside the probe can be leeched out. Which can damage the bulb and the sensor (1). Further more, storing the probe in the wrong type of storage solution can also cause the balance and composition of the solution inside the bulb to change. Which is why you should always use the storage solution that the manufacturer recommends. A few drops of water in the cap will help maintain a moist environment in the short term, and any leeching of the solution in the bulb should be minimal due to the minimal contact between the bulb and the water... but the bulb can dry out over time. Which is why for long term storage, it should be submerged in the recommended storage solution. Would you say the above three paragraphs are correct? I do have one follow up question, which I've never been able to find a definitive answer to... (1) Does the solution inside the bulb drying or having it's electrolyte levels reduced actually damage the bulb / sensor, or does it just make it inaccurate?

@@WebeloZappBrannigan The above three paragraphs are correct, very well written. For the follow-up question, the electrolyte inside the glass bulb (inner reference solution) will not be dried out and it won't be reduced, as it's sealed inside and does not contact anything. What will be reduced is the outer reference electrolyte, which contacts with and slowly goes into your tested solutions. When we talk about a pH probe's aging problem, the lack of outer reference electrolyte and the reduced sensitivity of the glass membrane are the two main reasons.

The bigger number is the actual real-time reading of the buffer. Usually, it won't be exactly 7.00 or 6.86, which is why the meter needs to be calibrated.

@@aperainst thank you much appreciated

It depends on how clean your rain water is. If the conductivity of your rain water is very low (

Please do not use any water to soak/store the pH probe as it will damage the probe over time. For soaking the probe, please use the 3M KCL solution.

@@aperainstboiled or bottled water?

@@isaiaguilera6279 Please do not use any water to soak/store the pH probe as it will damage the probe over time. For soaking the probe, please use the 3M KCL solution.

A few water droplets in the probe cap is totally fine and helps prevent the probe from being dried out. But never soak the probe in pure water. Only use 3M KCl for soaking.

Storage practice ranking from worst to best: soaking in pure water < store dry < store with a few droplets in the probe cap < soaking in pH buffer < soaking in 3M KCl

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