Reagents

For the Scuba II digital meter, select only tablets labeled Photometer that dissolve slowly without causing cloudiness. If you use Lovibond's Scuba II pool photometer, you need DPD 1 Photometer tablets for free chlorine, Phenol Red Photometer for pH, CyA-Test for cyanuric acid and Alka-M for alkalinity. Do not use Rapid-type tablets, as they contain insoluble binders that affect the sensor's optical transmission and produce false turbidity positives.

The main difference lies in the chemical fraction of disinfectant each reagent measures in the analysis vial. DPD 1 quantifies available free chlorine through an immediate reaction that produces a magenta color change proportional to the active disinfectants. In contrast, the DPD 3 tablet is added directly to the same sample, already colored by DPD 1, to release combined chlorine or chloramines, thereby determining total chlorine. By subtracting the free chlorine value from the total chlorine value, you can accurately determine the level of irritating chloramines in the water.

Investing in professional-grade analytical tablets for advanced equipment is essential if you require instrumental reproducibility under strict regulatory standards. When calibrating continuous measurements with the Lovibond MD200 3-in-1 photometer for chlorine, pH and cyanuric acid, photometer-grade tablets guarantee:

• Certified optical tolerance for specific wavelengths.
• Complete dissolution with no residue to scratch the glass vials.
• Watertight chemical protection in a push-through aluminum blister.
• Measurable chlorine range from 0.01 to 6.0 mg/l without analytical drift.

Tablet reagents should be stored in a cool, dry place, away from direct sunlight, at a stable temperature of between 10 °C and 25 °C. Keep the tablets in their airtight protective aluminum foil until the moment you use them. If the foil is punctured or the tablet looks brownish or lumpy, discard it immediately because it has reacted with ambient moisture and will produce inaccurate water test results.

The chemical reaction of the CyA-Test reagent requires actively crushing the tablet with a clean stirring rod inside the cuvette to create the necessary turbidity. Unlike Phenol Red or DPD 1, this reagent creates a uniform milky suspension that attenuates the photometer’s light beam to measure the stabilizer. If you do not crush the tablet completely within two minutes, the photometer will record a cyanuric acid concentration lower than the actual value.

Standard test strips are completely incompatible with digital cuvette photometry technology. A photometer works on the principle of spectrophotometry: a beam of light passes through a homogeneous liquid vial with a thickness of 10 or 24 mm, and the sensor measures light absorbance. Dip strips use absorbent pads for subjective visual readings, so inserting them into an optical cell destroys accuracy and blocks the light beam.

This phenomenon is known as indicator bleaching and occurs when the free chlorine concentration in the sample exceeds 10 mg/l. The massive excess of oxidizer destroys the chemical structure of the DPD molecule before the photometer completes the reading. In these circumstances, you should perform a controlled dilution:

• Use a dosing syringe to take 5 ml of pool water.
• Add 5 ml of distilled or deionized water to the cuvette.
• Add the photometric tablet and repeat the measurement process.
• Multiply the reading by two to find the actual value.