The Salifert Oxygen Test Kit (O₂ or Oxygen Profi-Test) is a colorimetric test kit designed to measure dissolved oxygen concentrations in aquarium water (freshwater, marine) or pond water.

Oxygen Test Kit it is designed to deliver results relatively quickly (“in just a few minutes”) given the chemical reaction scheme.

Because oxygen has relatively low solubility in saltwater, especially compared to freshwater, monitoring dissolved O₂ is particularly relevant in marine/reef systems.

Oxygen is highly essential for all life forms. Especially corals and marine fish require oxygen concentrations at saturation level. This is because of the low solubility of oxygen in saline water which is approx. 5 - 7 ppm.

The oxygen test measures oxygen concentration in just a few minutes.

Approx. 50 tests per kit. Range: 2- 14 ppm.   

The kit measures dissolved (free) molecular oxygen in water (i.e. O₂ in solution). It does not (in general) capture oxygen bound in other chemical species or oxygen within solid particulates.

The result is expressed in mg/L (ppm) O₂. For example, if your sample color matches the chart at 7 mg/L, that is your dissolved oxygen concentration.

In a marine (saltwater) environment, target or desirable dissolved oxygen levels are often somewhat lower than in freshwater because of lower solubility; many sources suggest maintaining at least ~6–7 mg/L in marine tanks.

In freshwater / pond systems, a typical guideline is to aim for 8 mg/L or higher (depending on temperature, species, and system parameters).

If the measured oxygen is low (near or below the bottom of the range), it indicates that oxygen is limited in the system. That can stress fish, corals, or invertebrates, especially under higher metabolic demand (night, feeding, temperature stress).

If the oxygen reading is very high (toward the upper end), that may be acceptable (depending on saturation limits) or might reflect conditions with strong aeration, photosynthesis, or recent oxygen injection. But if the reading is off-chart or anomalous, it may also reflect an error in test procedure or reagent issues.

How to use Oxygen Test Kit

1. Fill the test vial with 5 mL of aquarium (or pond) water.

2. Add 5 drops of reagent O2-1. Gently swirl or invert for ≈ 20 seconds to mix. It is important not to shake vigorously, because that could artificially alter the oxygen concentration by gas exchange.

3. Add 6 drops of reagent O2-2, swirl gently for ~15 seconds, and then let the mixture stand. For marine water, you wait 5 minutes; for other types (freshwater, pond), wait ~1 minute.

4. After the waiting period, add 6 drops of reagent O2-3, swirl gently (for ~20 seconds) to mix.

5. Allow about 30 seconds for color development.

6. Place the test vial against the white portion of the color scale/chart (provided with the kit) and compare the color by looking from directly above. The closest match gives you the dissolved oxygen reading in mg/L. If the sample color is intermediate between chart values, you may interpolate.

Strengths:

• Provides a direct measure of dissolved oxygen rather than relying purely on guesswork or proxy indicators.

• Relatively fast (~few minutes) compared to some laboratory techniques.

• Useful in systems where oxygen is a limiting factor (crowded tanks, high temperatures, CO₂ injection, reactors, sump designs with low flow).

• Works for marine, freshwater, and pond environments.

• Helps you identify when oxygen levels are dangerously low before animals are visibly stressed.

Limitations:

• It is a chemical/colorimetric test, so color perception, lighting, and background (white card) affect reading accuracy.

• The reaction and reagent stability can drift over time—expired reagents or degraded chemicals may produce errors.

• The kit measures free dissolved oxygen; it won't account for oxygen “locked” or bound in chemical species or in microbubbles that haven't equilibrated.

• The test must be done carefully (in terms of mixing, waiting times, gentle handling) because oxygen concentrations are sensitive to gas exchange with the air or agitation.

• The range is 2–14 mg/L; if oxygen falls below 2 or exceeds 14 mg/L, the kit may not reliably show the actual value (you may just see “below range” or “above range”).

• Temperature and salinity influence oxygen solubility; the test does not automatically correct for those, so one must interpret in the context of system conditions.

• In very low-oxygen situations, color development might be faint or ambiguous, making it harder to match to the color chart.

Practical Tips

• Use fresh, uncontaminated water samples and ensure the test vial is clean and free from foreign substances.

• Avoid introducing bubbles during sampling or reagent addition, as trapped bubbles can distort oxygen concentration readings.

• Perform tests under consistent lighting and always use the white background from the kit to aid color comparison.

• If you see an ambiguous color, consider repeating the test or averaging multiple trials.

• Track oxygen levels over time (e.g. daily or at times of stress) rather than relying on single isolated readings.

• If oxygen readings are low, improve aeration, water movement, gas exchange (e.g. surface agitation, powerheads, air stones) or reduce respiration loads (less feeding, fewer animals).

• Use this test in conjunction with other parameters (temperature, salinity, pH, CO₂ load, nitrates, etc.) to understand the full picture of the system’s gas balance.

• Always follow safety instructions: some reagents (e.g. O2-1) can be irritating—avoid contact with skin or eyes, wash thoroughly if contact occurs, and keep kit away from children.