Hanna pH 4.01 Calibration Solution HI7004L | 500 mL (16.9 oz)

Hanna pH 4.01 Calibration Solution for Pens, Meters and Probes

Hanna's HI7004L is a buffer used as the acid point when calibrating a pH pen, a portable meter or an inline controller probe. Each bottle holds 500 mL, about 16.9 fl oz, which covers weekly checks across several meters. The value is 4.01 pH at 25°C, held to ±0.01 pH, and every batch is standardized against NIST reference materials. The chemistry is a potassium hydrogen phthalate buffer, the classic acid standard for glass pH electrodes. A pH-versus-temperature chart is printed on the label, so a cold reservoir room or a warm propagation tent does not throw off the reading. The label also carries the lot number and the expiry date. Unopened, Hanna rates the solution for 5 years from manufacture. Once the cap comes off, plan on roughly 4 to 8 weeks of reliable use. The formula contains no dyes that could stain the electrode's reference junction. That pairing of a traceable value and a printed temperature table is what makes a two-point calibration repeatable.

Using a pH 4 Buffer Solution for Two-Point Meter Calibration

Most growers run a two-point calibration, setting the meter at pH 7 first and then at this acid point. Hydroponic and coco feeds usually sit between pH 5.5 and 6.5, so a 4-and-7 calibration brackets the range that matters. Pour a small amount into a clean cup rather than dipping the probe in the bottle. Rinse the electrode with distilled or RO water between buffers, then blot it dry rather than wiping. Discard the used portion afterward, since pouring it back contaminates the rest. Recap the bottle right away and store it out of sunlight and away from heat. Weekly calibration suits most rooms, while daily checks make sense when an automated doser depends on the reading. A meter that will not settle on this point usually has an aging probe, not a bad buffer. Keep a pH 7 standard and an electrode storage solution alongside it to complete the routine. Writing the opening date on the label makes the usable window easy to track.

Key Features

• NIST-traceable value: Each batch is standardized against NIST reference materials, so a calibrated meter agrees with lab instruments.
• Temperature chart on label: The printed table gives the true buffer value at room temperatures above or below the reference point.
• Lot and expiry marked: Every bottle shows its lot and expiry date, so an outdated standard is easy to spot on the shelf.
• Dye-free formula: Nothing in the solution stains or clogs the electrode's reference junction over repeated calibrations.
• Universal acid point: Works as the low calibration point for pH pens, portable meters, benchtop units and controller probes.

Technical Specifications