Product Description Protect You & Your Family's HealthIdeal for Household or Laboratory Use, Suitable for Testing Ph Balance of Drinking Water, Pool, Aquarium, Ro System, Spa, or Hydroponics; Appropriate for Wide Range of Applications. Instructions for use of PH calibration powder: Calibration powder: pH standard solid substance. It can be used after adding water. Suitable for the calibration of any type of ph meter. Each package can prepare 250ML standard solution.(Be sure to add water according to the required ratio, otherwise it will affect the accuracy of the calibration and increase the error) Questions & Answers: 1. Q: How often should I calibrate my ph meter pen ? A: One calibration can last for about half a month. When the electrode exposed to air for extended period of time, users should calibrate it. When testing polluted water quality, more frequent calibration is required to ensure the accuracy of the test value 2. Q: Can I test two kinds of water without calibrating ? A : Yes , but when testing the liquid that is not pure water or distilled water, after the test, you need to put it in pure water or distilled water, wash it and wipe it dry, and then test the next liquid (to ensure the accuracy of the value of the next test liquid) 3. Q: Why my ph meter switch and digital display are not sensitive ? A: It might be caused by low battery. Just replace the battery and it will work again. 4. Q: Can I use this to test Urine A: Yes , it can. The test liquid must not be corrosive, which will damage the accuracy of the glass probe and shorten the service life of the glass probe. 5. Q: What if the calibration result is wrong? A: Assuming that the calibration result is wrong, the pen recognizes ph 9.18 or ph 4.01 after calibrating ph 6.86 . Step 1: Take 50ml of purified water or distilled water, and then import one pack of 6.86 calibration powder, stir evenly, put the PH pen probe in water for One Hours. Step 2: Then turn on the pen, press and hold the CAL button for five seconds, then let go, the value flashes, and the END calibration is completed.Except the ways above, you could long press the switch and calibration keys at the same time for five seconds, restore the factory settings, and then test.( The test difference might within 2% with reset control , and the powder calibration's test difference is within 0.1%-1% ) Please Note:Clean the electrode with distilled water every time before and after use. Don't touch the electrode by hard tools or fingers. Always replace the protective cap to keep electrode from drying out.Please do not immerse the meter into the solution over the "warning line", to avoid damage to the circuit board.When the meter cannot be turned on or the display fades, open the battery case and replace battery (pay attention to the polarity), then need to recalibrate the meter.