APERA INSTRUMENTS / YD300 / AI4731

Water hardness by electrode.
Read it like pH.

The YD300 measures total water hardness, the combined calcium (Ca²⁺) and magnesium (Mg²⁺) concentration, with Apera’s 601-S 3-in-1 hardness electrode: measuring, reference and temperature elements in one body. Apera states the electrode method has been proven to give results consistent with EDTA titration, without titrant, indicator or end-point reading; you calibrate, dip and read.

It reads 0–10 mmol/L and displays the result in eight hardness units, from mg/L as CaCO₃ to German, French and English degrees. The kit includes B1, B2 and B3 calibration solutions, activation solution, six 20 mL test cups and a pedestal in a rugged carrying case. The meter is IP57 rated and runs on two AA batteries.

Know what arrives
in the carrying case.

Kit list follows Apera’s YD300 instruction manual, section 7.

Prepare the electrode.
No bubbles in the head.

Before each use, shake the 601-S firmly so the inner solution drops into the measuring head; there must be no air bubbles in it. For first use, pour a little activation solution into the soaking cup and soak the electrode for at least two hours. An electrode in regular use needs about half an hour. Readings during activation are random; start once they settle.

Pour small amounts of B2 and B3 into their labeled cups and stand the cups in the pedestal to avoid spills. After measuring, rinse the electrode in distilled or deionized water and store it in its protective cap.

Calibrate at two points.
Pick the pair for your water.

Two calibration modes are available. B2/B3 (2.00 × 10⁻¹ and 2.00 mmol/L) is for general water. B1/B2 (2.00 × 10⁻² and 2.00 × 10⁻¹ mmol/L) is for low-hardness water below 2.00 × 10⁻² mmol/L, such as boiler water. Press CAL, and the flashing B icon tells you which solution to use; rinse, dip, stir for a few seconds, let it stand, and press CAL when the stability icon stays on. Each point finishes in about 20 seconds.

Then read B2 as a sample. The result should be 2.00 ± 0.25 × 10⁻¹ mmol/L; if it is not, repeat the calibration. A new electrode needs to be calibrated twice, and the meter does not recognize the standards on its own, so follow the icon. The B solutions are unbuffered and contaminate easily, B1 most of all; Apera suggests replacing them after four to five uses.

Dip, stir, read

Rinse the electrode, insert it in the sample, stir gently and let it stand. Take the reading when the stability icon stays on, and press the UNIT key to switch units. Test dilute samples before concentrated ones and keep separate containers for each.

Above 10 mmol/L

When the sample exceeds 1.00 × 10 mmol/L, an icon prompts you to dilute it tenfold. Measure the diluted sample and multiply the reading by 10. An activity-compensation setting, on by default, applies from 4.00 to 10.0 mmol/L.

Boiler water

Use B1/B2 calibration and add sodium bicarbonate as an ionic strength buffer to B1, B2 and the soaking solution: 50.4 mg of ACS-grade NaHCO₃ per 100 mL. Apera notes that skipping it causes a significant error.

Report in the unit you need.

The meter displays eight units: mmol/L, mg/L as CaCO₃ (also called ppm or U.S. degrees), mg/L as CaO, mmol/L (boiler), mg/L as Ca, and French (°fH), German (°dH) and English (°eH) degrees. One mmol/L equals 100 mg/L as CaCO₃, 40.1 mg/L as Ca, 10 °fH, 5.6 °dH and 7.0 °eH.

Matching full-scale ranges are 0–1000 mg/L as CaCO₃, 0–561 mg/L as CaO, 0–401 mg/L as Ca, 0–20 mmol/L (boiler), 0–100 °fH, 0–56 °dH and 0–70 °eH. Resolution is 0.01 or 0.1 hardness unit, set in the parameter menu.

Read the display at a glance.

Readings use scientific notation, so 2.00 with 10⁻¹ above it means 2.00 × 10⁻¹. The display also shows the unit, the sample temperature, a stability icon that stops flashing when the reading is steady, the B1/B2/B3 solution prompt, Cal 1 and Cal 2 icons, and a low-battery warning.

Five keys run the meter. Short-press M+/RM to store a stable reading with its number, unit, temperature and calibration mode; long-press it to recall. Up to 99 readings are kept. The backlight turns off after 8 minutes and the meter after 10 minutes without a key press; both can be switched off in the settings.

Check the specifications.

Apera specifies accuracy of ±5% FS, with automatic temperature compensation from 5 to 50°C. The temperature reading covers 0–60°C at 0.1°C resolution, ±0.5°C.

Operate the meter at 5–35°C and up to 85% relative humidity. It measures 65 × 120 × 31 mm, weighs 180 g, runs on two AA batteries and is IP57 rated. Replacement parts include the 601-S electrode, B1/B2/B3 solutions in 100 mL or 250 mL bottles, activation solution, test cups and the pedestal.