Calibration fluid PH 4.01 20ml

A 20 ml sachet of buffer at exactly pH 4.01. Your second calibration point, and for growers the right one.

Once your meter is set on 7.01, a second point corrects the slope of the scale: the ratio by which the electrode converts voltage into pH units. That ratio shifts as a membrane ages, and without a second point you never see it.

Why 4.01 rather than 10.01

Most meters let you choose between 4.01 and 10.01 as the second point. For growing that is not really a choice.

A calibration is most accurate between your two points, and less so outside them. You work at 5.5 to 6.2 in hydroponics and coco, and 6.0 to 6.5 in soil: all on the acidic side of 7.

Calibrate on 7.01 and 4.01 and your entire working range sits neatly between your two points. Calibrate on 7.01 and 10.01 and it falls completely outside, leaving your meter to extrapolate. Which is why 4.01 is the standard second point in horticulture, and 10.01 is mostly a laboratory value.

Technical Specifications:

• Value: pH 4.01
• Volume: 20 ml
• Use: second calibration point, after 7.01
• Handling: single use; do not pour back

Frequently asked questions

In what order do I calibrate?
7.01 first, then 4.01. Rinse the tip with clean water in between.

Do I need 10.01 as well?
Not for growing. That exists for measuring in the alkaline range.

Why will it no longer calibrate on 4.01?
If the zero point at 7.01 is fine but 4.01 cannot be reached, the slope has drifted. That usually means your electrode needs replacing.