Bluelab pH 4.0 & 7.0 Calibration Solution Kit - pH Meter & pH Pen Calibration for Balanced Nutrient Solution NIST Traceable | Hydroponics, Gardening & Growing Tents (500 ml/ 16.9 Fl Oz Each)

I followed the directions to the letter and the calibration solutions worked perfectly. I feel so much better about my grow knowing the reading I am getting are true readings. The solution hand my Blue Labs OnePen with perfectly calibrated and fast results

I own the blue lab ph pen and EC meter, and these solutions are perfect for calibration of the pH pen. I bought large bottles, still working super well a year later, probably have enough to last me another 3 years of regular monthly calibration checks/calibrations. Between the nice test pen and these solutions my hydroponic results have improved. Good stuff.

Fast delivery, quality products

I do not dislike anything about this product is my first time using this product with a blue lab pH pen I’ve got to say it’s worth the money both these are 16.9 fl oz. This will probably last me the next 12 months.

Works perfect for recalibration of blue lab ph pen. What else could you ask for?

The accuracy,easy of use and storage is why this works for me..

This product help alot to ensure my ph meter was kept in good condition. Good buy!

Both bottles state to use up within 3 months of opening. If you’re only calibrating one pen per month this won’t happen. What is the impact on calibration accuracy after 1 or 2 years with these solutions?