We made the Benchmark Calcium & Magnesium Test Kit because we were frustrated with the tests we were using.
We test water from our own reef systems and from customer aquariums. Too often, a calcium or magnesium result left us with another question: was the number real, or did we read the colour change differently this time?
That matters when the next step might be changing a dose. We wanted a test with a clear endpoint, a straightforward procedure, and results we could repeat. So we started working on our own.
A test we built for everyday reefkeeping
The first version was for use at New Dawn, not for sale. We adjusted the reagents, sample size, colour changes, and calculations while testing real saltwater from our systems and customer tanks.
We also compared our readings with ICP results whenever we had matching samples. ICP gives a much broader lab analysis, while this kit is made for regular testing at home. Comparing the two helped us catch problems and improve the method.
Once we had a test we were comfortable using ourselves, we turned it into the Benchmark Calcium & Magnesium Test Kit.
Why calcium and magnesium are tested together
Calcium helps corals build their skeletons. Magnesium supports the balance of calcium and alkalinity in seawater. Looking at them together gives you a better picture than treating either number on its own.
The kit uses two fresh 5.00 mL water samples:
- The first test measures calcium.
- The second test measures calcium and magnesium together.
- The magnesium calculation uses both syringe readings to account for the calcium already measured.
That is why the calcium test is completed first and why you need a fresh sample for each test.
How the calcium test works
Add Calcium Buffer and a level scoop of Calcium Indicator to a fresh 5.00 mL sample. The sample will turn pink-orange. Add Calcium Titrant slowly while swirling until the whole sample reaches a stable purple colour.
Calcium (ppm) = Calcium Titrant used (mL) × 600
Slow down as the colour starts to change. Small additions and steady swirling make the endpoint easier to see.
How the magnesium test works
Start with a second fresh 5.00 mL sample. Add Magnesium Buffer and two drops of Magnesium Indicator. The sample will be wine red. Add Magnesium Titrant slowly while swirling until the whole sample is pure blue with no red or purple left.
Magnesium (ppm) = 1,944.40 × Magnesium Titrant used (mL) − 363.87 × Calcium Titrant used (mL)
The formula is longer because the second test reads calcium and magnesium together. Your calcium syringe reading is used to remove the calcium portion and calculate magnesium.
Everything has a place
We designed the reusable case to make the testing routine easier to follow. The procedures and quick-read scales are printed on the case, and the stand keeps the reagents, syringes, vials, and scoop organized.
The complete kit includes:
- 118 mL Calcium Buffer
- 20 g Calcium Indicator powder and a level scoop
- 118 mL Calcium Titrant
- 59 mL Magnesium Buffer
- 7.5 mL Magnesium Indicator
- 118 mL Magnesium Titrant
- Two sample vials
- Four 1 mL syringes
- A reusable testing stand with the procedures and quick-read information printed on it
A few tips for better results
Use two fresh samples
Do not reuse the calcium sample for the magnesium test. Each test needs its own fresh 5.00 mL sample.
Keep the syringes with their matching reagents
Use each labelled syringe only with the reagent named on it. Rinse the sample vials after testing, and do not pour unused reagent back into a bottle.
Slow down near the endpoint
Add titrant in smaller amounts as the colour begins to change. Swirl thoroughly and make sure the entire sample has changed colour before recording the result.
Repeat an unexpected result
If a number does not make sense, run the test again before making a large dosing change. Compare it with your recent results, salinity, and dosing history.
Where this kit fits
This kit is made for routine calcium and magnesium checks between ICP tests. It can help you establish a baseline, watch how your reef is using these elements, and confirm that a dosing change is having the effect you expected.
ICP testing is still valuable because it measures a much wider range of elements. This kit has a simpler job: give you useful calcium and magnesium readings at the aquarium, whenever you need them.
We built it because we wanted a test that felt clear and dependable in our own hands. Now it is ready for yours.
Test first, then dose.
View the Benchmark Calcium & Magnesium Test Kit · View Calcium & Magnesium Refill Reagents · Explore Benchmark
Safety: Calcium Buffer contains 4% sodium hydroxide. Read every product label and SDS, wear suitable eye and hand protection, and keep all reagents out of reach of children.
