Calibration fluid PH 4.01 100ml

A 100 ml bottle of pH 4.01 buffer, the second calibration point alongside 7.01. Enough for dozens of calibrations.

7.01 sets your meter's zero point; 4.01 corrects the slope of the scale. Together they bracket exactly the range you grow in.

How much do you actually use?

This question comes up more than you would expect, and the answer decides whether you want sachets or a bottle.

Per calibration you need no more than a shallow pool in a small pot: just enough to submerge your electrode tip. In practice that is somewhere between 10 and 20 millilitres, depending on your pot. So a 100 ml bottle covers roughly five to ten calibrations.

Calibrating monthly (the usual rhythm for a pH meter in use) this bottle lasts you something like six months to a year. Provided you use the liquid sparingly and cleanly: never calibrate in the bottle, and never pour back.

What pushes your usage up are the things that pay for themselves: recalibrating after cleaning your electrode, and recalibrating whenever you distrust a reading. Do those anyway.

Technical Specifications:

• Value: pH 4.01
• Volume: 100 ml
• Use: second calibration point, after 7.01

Frequently asked questions

Do I need both 4.01 and 7.01?
If your meter calibrates at two points, yes. With single-point calibration you only need 7.01.

Why not just calibrate in the bottle?
Because your electrode always carries something over from what you have been measuring. Calibrating in the bottle once can ruin your whole supply.

How do I know it is still good?
Note the opening date. If calibration suddenly behaves oddly, an old bottle is as much a suspect as a worn electrode.