Question 1

I have purchased 2 of these, why are they so inaccurate?

Accepted Answer

If you calibrate ANY PH meter using the mix it yourself "calibration" solutions, accuracy will be impossible. I just purchased this meter set, and discovered the distilled water I use was ph4 and below! I have the "other" style cheap meter, that has proven very stable for me, and after checking it in GHP 7.0 calibration solution, used it to test the accuracy of this relentlessly poor example of a ph testing system. 
First off, the solution instructions make no mention what the ph of the distilled water needs to be. My 4.0 water mixed with the 4.0 and 6.86 powder, resulted in a solution of 3.3 and 6.0 instead, so IMO, the MIY calibration solutions are a joke, as are ph meters that calibrate on the 6.86 standard instead of 7.0.

Question 2

If i use a 7.0 calibration solution will the automatic calibration be off by .14 since it comes with a 6.86 calibratind powder?

Accepted Answer

Yes! I recently calibrated with 7.0. Prior to calibration, it read the 7.0 solution at 7.0, calibrated with 7.0 solution it now reads 7.18. Find the correct calibration solution

Question 3

If my tap water is between 6.5 and 7.0 ph do i need to add the ph up and down liquid i bought for indoor cannabis grow? What about ppm?

Accepted Answer

If you’re growing in soil 6.5 is perfect if you’re growing in Hydro/water do you want to be around 5.8 say you’re at 7.0 PH I would just add a couple drops per gallonTo get it down two around 6.5

Question 4

If I choose EC, does it retain the setting after power cycles?

Accepted Answer

Yes, but my meter randomly switched back to TDS.  The "EC" does not show a decimal, and the numbers are too close to TDS. If you don't pay attention, you will hurt your plants.

Do not purchase.

ASIN	B06XKMH86J
Brand Name	VIVOSUN
Customer Reviews	4.1 4.1 out of 5 stars (22,998)
Item Weight	0.1 Kilograms
Manufacturer	VIVOSUN
Material Type	Plastic
Model Number	4336465266
Part Number	4336465266
Recommended Uses For Product	Aquarium, Home Water, Swimming Pool, Water Test
Sterility Rating	0-14
UPC	615435160962

VIVOSUN pH & TDS Meter Combo 0 05ph High Precision Pen Type pH Meter & +/- 2% Readout Accuracy 3-in-1 TDS EC Thermometer TDS + PH

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