The Salifert Strontium Test Kit is a chemical (colorimetric / titration) kit designed for marine aquaria / reef systems to estimate the concentration of strontium in seawater. (Marine use only)

Strontium is an element that shares some chemical similarities with calcium and is often considered beneficial (or at least desirable) in reef systems, because corals and calcareous algae incorporate strontium (to some extent) into their skeletons/shells.

The kit measures both ionically free strontium and moderately complexed strontium (i.e. strontium bound in intermediate complexes) in discrete increments

Salifert notes that strontium is relatively difficult to measure chemically because of interference and overlapping chemistry with calcium, so the procedure is more complex and error-sensitive than simpler tests.

Strontium plays an important role by accelerating coral and calcareous algae growth.
NSW contains approx. 7 – 9 mg/L strontium.
Since the growth of corals and calcareous algae goes hand in hand with strontium and calcium depletion, depletion of calcium usually means depletion of strontium as well.

It is advisable to maintain a strontium concentration between 5 and 20 mg/L.

Strontium measurement is a necessity but is unfortunately a relatively difficult test. Perhaps in forthcoming years this will change when newer and easier methods for strontium measurement will become available.

It therefore is a test, which many hobbyists will not conduct frequent enough.

For that particular reason strontium additives should be designed in such a way that a too low or a too high strontium concentration is avoided.
With the Salifert Natural-Strontium additive we have reached this aim.
When used in combination with our Coral Calcium additive according to the instructions then the need for strontium measurement is greatly reduced and would have to be performed only once every few months.
Furthermore NSW contains strontium associated with sulfate. This form lacks the toxicity, the commonly used, strontium chloride has.
We therefore use predominantly strontium sulfate together with some other ingredients to avoid the occurrence of an ionic imbalance. It also makes it more effective and less toxic than strontium chloride.
The Salifert strontium test kit detects both ionically free and moderately complexed strontium. Salifert was the first to introduce a strontium test kit.

The kit quantifies the concentration of dissolved (free + moderately complex) strontium in your aquarium’s seawater, in units of mg/L (ppm).

Because strontium is chemically similar to calcium and is often co-depleted when calcium is consumed (e.g. by corals), a decline in calcium may hint that strontium is also being drawn down.

A measured value significantly lower than natural seawater (e.g. < 5 mg/L) would suggest strontium depletion, which might indicate that supplementation or water changes are needed.

A significantly higher reading might suggest over-dosing or interference / measurement error, but in practice most reef setups stay near the natural seawater levels (7-9 mg/L) unless supplemented heavily.

Because of the chemical complexity and potential interference (especially from calcium), the absolute precision of the strontium reading can be limited. The kit is best used to monitor relative changes or verify that your strontium remains within a safe band, rather than expecting lab-level accuracy.

How to use Strontium Test Kit

1. Use a clean test vial and fill it with 5 mL of aquarium (or reef) water (using a 5 mL syringe).

2. Add 12 drops of reagent Sr-1 (a caustic reagent) and swirl gently for about 10 seconds. Be cautious as this reagent is caustic.

3. Add 1 level scoop of Sr-2, swirl gently (≈ 5 seconds). At this stage the sample should turn a red or pink color.

4. Take a 1 mL syringe (the one without the yellow label, fitted with the small plastic tip), draw 1.00 mL of reagent Sr-3 (up to the black rubber ring), and add it fully to the test vial. Swirl gently for ~20 seconds. If the color turns blue immediately and stays blue even after 30 seconds, that suggests the calcium concentration is extremely low (e.g. ~300 mg/L or less), and you may need to correct calcium before proceeding.

5. If the color is not fully blue, repeat: draw another 1.00 mL of Sr-3 and add drop-wise (i.e. one drop at a time), swirling gently after each drop, until the sample turns blue. Once blue, swirl ~15 seconds and if the color tends to revert, you might need one extra drop to stabilize it. Then read the value on the syringe’s black rubber ring (that reading corresponds to a calcium value via a calcium table).

6. Next, fill the alternate 1 mL syringe (the one with the yellow label, no plastic tip) to 0.50 mL of reagent Sr-4, and add this to the test vial, swirling gently (~10 seconds). The color shifts again (often toward red / pink).

7. Add two level scoops of Sr-5 (powder reagent), swirl gently until dissolved, then allow the mixture to stand 12–15 minutes undisturbed.

8. After the waiting period, use the same syringe (without yellow label, with plastic tip) to draw 1.00 mL of Sr-3, and then add it gradually (drop by drop), swirling gently (~20 sec per drop), until the color again turns blue. At that endpoint, read the value (on the syringe’s rubber ring) and refer to the strontium table in the instruction sheet to get the strontium concentration.

Because of the titration method and color change behavior, the color transition from pink/red to blue is relatively sharp (occurring over a small range), so you must watch carefully and stop once the full change is achieved.

Strengths:

• The kit allows hobbyists to test strontium in reef tanks, which is harder to measure than some common elements (e.g. calcium or alkalinity).

• It measures not only free ionic strontium but also moderately complexed forms, giving a more comprehensive estimate (within chemical constraints).

• Useful for trend monitoring — seeing whether your strontium is stable, depleting, or being over-supplemented.

• Allows you to check whether your dosing (if you supplement strontium) is maintaining target levels.

Limitations:

• Because of chemical overlap between calcium and strontium, the test requires a preliminary calcium titration step, which introduces cumulative error.

• The color change (pink → blue) happens sharply over a narrow concentration range (~10–15 ppm shift in calcium/pH equivalent) which means mis-judging the endpoint by even a drop can produce noticeable error.

• Color interpretation is subjective: lighting conditions, observer perception, slight hue shifts can lead to error.

• Reagent instability or degradation can impact accuracy (expired or improperly stored reagents may give incorrect results).

• Because it is a manual titration method, it’s more labor-intensive than many simpler test kits (e.g. dropping reagents, multiple steps, waiting times).

• The kit’s resolution (increments of 5 ppm or similar) is not extremely fine; it may not discern small fluctuations extremely precisely.

• In very low calcium or disequilibrium systems, results can be unreliable; the test assumes that the calcium concentration is within certain normal ranges.

Practical Tips 

• Carefully follow each step and timing precisely — do not rush, because the titration endpoint is sharp.

• Use clean vials, syringes, and equipment; avoid contamination from residual reagents or salts.

• Perform the test under consistent lighting (ideally daylight / neutral white light) and against a white background so color changes are easier to discern.

• Add dropwise slowly as you approach the color change; swirl gently and wait briefly to let the reaction fully evolve before adding the next drop.

• Watch for color reversion (i.e. if after turning blue it drifts back) — you may need one extra drop to stabilize the endpoint.

• If your calcium is very low or abnormal, solve that first, because the strontium test assumes your calcium is reasonable.

• Repeat the test a couple of times to confirm consistency, especially when first using the kit.

• Use this test in trend mode — monitoring whether strontium is trending upward or downward — rather than relying on a single absolute value.

• If you supplement strontium, test before and after dosing to see the effect and to ensure you're not overshooting.

• Store reagents properly (cool, dark, dry) and pay attention to expiration dates to minimize drift or reaction degradation.

• Keep your observation consistent (same time of day, same lighting) to reduce variability.