Red Sea Magnesium Pro Testing Kit 100 Tests

• 100 tests per kit – the largest test count in Red Sea's Pro foundation range, which suits a parameter you check fortnightly rather than daily.
• 20 ppm resolution – meaningful against targets of 1100 to 1350 mg/L, where a broad colour kit reads the same at 1150 and 1300.
• Titration with a powder reagent step – a dosing spoon and two liquid reagents set the sample up, then you titrate to a clear colour break.
• Single-hand titrator – one hand meters, the other swirls, so the endpoint is where the chemistry says it is rather than where your grip gave out.
• Meters Foundation C directly – the reading maps onto a dose of Red Sea's magnesium supplement rather than a general recommendation.
• Reagent refills available – part R21416 restores all 100 tests and keeps the titrator, spoon and glassware in service.

• Single-hand high-precision titrator
• Reagent A, 25 mL
• Reagent B, 25 mL
• Titrant, 75 mL
• 5 mL syringe
• Dosing spoon
• Analytical-grade glass vials
• Colour reference card
• Instruction manual
• Chemical-resistant plastic storage case

• Any magnesium supplement. Unlike the alkalinity kit, no sample bottle ships with this one – Red Sea Foundation C (Magnesium) is a separate purchase.
• Calcium and alkalinity tests. Those are the Calcium Pro and KH/Alkalinity Pro kits.
• A salinity meter. Magnesium tracks with salinity, so a reading taken at the wrong specific gravity is misleading rather than merely imprecise.

Red Sea publishes foundation targets by system type in its Foundation Supplements manual. Magnesium is set proportionally to the calcium and alkalinity you are holding, which is why all three appear together here.

At 20 ppm resolution, the gap between the mixed reef and SPS targets is about three and a half increments – wide enough that this kit can actually tell you which programme you are running.

Below your target

Dose Red Sea Foundation C, which is the supplement this kit exists to meter. Magnesium moves slowly and is consumed slowly, so correct it over days rather than in one hit.

Above your target

Stop dosing. Magnesium has no fast removal route in a reef aquarium, so the only practical correction is water changes with a salt mixed to your target, and time.

Calcium or alkalinity will not hold

This is the classic symptom of low magnesium and the main reason to own this kit. Bring magnesium back to target first, then re-test the other two – they often correct themselves once magnesium is right.

Level the dosing spoon. The powder step is measured by volume, and a heaped spoon shifts the endpoint further than the kit's 20 ppm resolution.

Rinse the glass vials in RO water between tests. Residual reagent from the previous test is the most common cause of a magnesium result that disagrees with the last one.

Store the reagents in their original containers, closed, cool, dry and out of direct sunlight, and away from acids, alkalis, oxidising compounds and metals. Reagent age is the usual explanation when two kits disagree with each other.

Red Sea's safety data sheet for this kit and its refill gives Reagent A the signal word Danger. Reagent A is classified as harmful if swallowed and harmful in contact with skin, causes severe skin burns and eye damage, and may be corrosive to metals. The named constituents are sodium tetraborate decahydrate at 1–5%, potassium hydroxide at 1–5% and oxalic acid at 1–5%. Reagents B and C carry no signal word.

Sodium tetraborate is classified as a reproductive hazard, so handle Reagent A with care and keep the kit out of reach of children. In the eyes, rinse with plenty of water for at least 15 minutes and get medical attention. If swallowed, do not induce vomiting – rinse the mouth thoroughly with water if the person is conscious, and get medical attention.

Suitable for: reef aquariums running a foundation dosing programme, anyone whose calcium or alkalinity refuses to stabilise, and anyone mixing their own saltwater who wants to confirm what the batch actually landed at.

Not suitable for: freshwater aquariums, where magnesium at these concentrations is not a parameter you manage. It also will not measure calcium or alkalinity, and it is not a substitute for correcting salinity before you test.

• Red Sea Magnesium Pro Reagent Refill – part R21416, restores all 100 tests without rebuying the titrator.
• Red Sea Foundation C (Magnesium) – the supplement you dose against the reading.
• Red Sea KH/Alkalinity Pro Test Kit – the parameter magnesium is usually blamed for.
• Red Sea Calcium Pro Test Kit – completes the foundation trio.
• Red Sea Coral Pro Salt 20 kg – mixes to elevated foundation levels, so water changes hold magnesium up rather than diluting it.
• Red Sea range – the rest of the Reef Care testing and supplement program.

Reagents are consumables and carry no service warranty. Any manufacturer warranty Red Sea offers applies in addition to your rights under the Australian Consumer Law, which are not limited or excluded by it. A kit arriving with leaking, damaged or out-of-date reagents is replaced.

Ships as a standard parcel. The reagent volumes are well under the threshold for dangerous goods handling, so no special freight applies.

How accurate is the Red Sea Magnesium Pro Test Kit?

Red Sea specifies a resolution of 20 ppm. Because it is a titration rather than a colour comparison, the reading is not bounded by a printed scale – you titrate to an endpoint and read the volume used off the titrator.

How many tests does the kit contain?

The Red Sea Magnesium Pro Test Kit contains 100 tests, supplied as 25 mL of Reagent A, 25 mL of Reagent B and 75 mL of titrant. The reagent refill, part R21416, restores the same 100-test count.

How often should I test magnesium?

Magnesium is consumed far more slowly than calcium or alkalinity, so fortnightly testing suits most reef aquariums. Test it immediately, though, whenever calcium or alkalinity start behaving oddly – that is nearly always a magnesium problem.

What magnesium level should a reef tank run at?

Red Sea's published foundation targets are 1350 mg/L for a mixed reef, 1280 mg/L for an SPS-dominant system and 1100 mg/L for marine fish only. Magnesium is set proportionally to the calcium and alkalinity levels you are holding, not chosen independently.

Does this kit include a magnesium supplement?

No. Unlike the KH/Alkalinity Pro kit, which ships with a 100 mL sample of Foundation B, the Magnesium Pro kit contains reagents and hardware only. Foundation C is bought separately.

My magnesium is too high. How do I bring it down?

There is no quick fix. Magnesium is not consumed fast enough or removed by any common filtration to drop on its own, so the practical correction is to stop dosing and do water changes with saltwater mixed to your target level.