DuvinDD 18 Pack pH Buffer Solution Powder for Precise pH of pH Meter, pH Calibration Solution Powder Packets pH 6.86/4.01/9.18

If you use the cheaper model pH test pens these are a must.Having to have fresh distilled water in hand that hasn't been opened is kind of a pain but is a necessary evil for proper calibration.

Easy to use and accurate

On multiple occasions now when I use them, my top shelf pH meters read different then what advertised.....Next purchase won't be this brand or store

IMHO, not worth the effort to return and reorder. Quality control???

Works as advertised. Easy to use. Just need distilled water and follow instructions and calibrate your pH meter per instructions Can keep standard for about a week, then mix new.

Great for recalibrating my ph pen.