Red Sea Reef Care Magnesium Foundation C
Cost per litre
Under 1c
Water type
Marine/Reef
Red Sea Reef Care Magnesium Foundation C
The element that lets calcium and alkalinity hold their levels. Red Sea Reef Foundation C is the ready-to-use liquid magnesium component of the three-part Reef Foundation program. When calcium and KH won't stay balanced no matter how carefully you dose them, low magnesium is nearly always the reason — it's the buffer that keeps calcium carbonate from precipitating out of solution.
Key features
- Precise dosing — 1 mL per 100 L (25 US gal) raises magnesium by 1 ppm.
- Stabilises Ca and KH — magnesium at the correct level is what allows calcium and alkalinity to be dosed accurately without one dragging the other down.
- Blend of magnesium salts balanced to the chloride/sulphate ratio found in natural seawater.
- Ready to use — no mixing, works with any dosing pump or manual routine.
- Pairs with Foundation A and B — part of the same three-part system.
Specifications
| Size | SKU | Dose for +1 ppm Mg | Form |
|---|---|---|---|
| 500 mL | RED282 | 1 mL per 100 L | Ready-to-use liquid |
| 1 L | RED282b | 1 mL per 100 L | Ready-to-use liquid |
| 5 L | RED282a | 1 mL per 100 L | Ready-to-use liquid |
Cost per litre
A 500 mL bottle carries enough to raise 50,000 L of tank water by 1 ppm magnesium; the 5 L pack raises 500,000 L by the same 1 ppm. At current prices that's about 58c per 1,000 L corrected on the 500 mL bottle, down to roughly 34c per 1,000 L on the 5 L pack — both round to under 1c per litre on the product tile.
| Size | Price | Litres raised 1 ppm Mg per pack | Cost per 1,000 L corrected |
|---|---|---|---|
| 500 mL | $29.00 | 50,000 L | $0.58 |
| 1 L | $45.00 | 100,000 L | $0.45 |
| 5 L | $171.00 | 500,000 L | $0.34 |
Dosage and directions
Magnesium moves slowly compared to calcium and KH — test fortnightly rather than daily, and correct gradually. Dose 1 mL per 100 L of tank water for every 1 ppm you need to raise, split over several days for any correction larger than about 20 ppm.
What magnesium level should I be targeting?
Reef tanks are typically run between roughly 1,250 and 1,350 ppm, which is the range that keeps calcium and alkalinity stable at natural seawater ratios. Test your own tank rather than assuming a single "correct" number.
Suitable for, and not suitable for
Suitable for marine and reef aquariums running calcium and alkalinity dosing, where magnesium needs to be corrected or maintained alongside them. Not a substitute for testing — magnesium is easy to overshoot if dosed on a schedule rather than to a result. Not intended for freshwater aquariums.
Safety
Keep out of reach of children and pets. Avoid prolonged skin and eye contact and rinse with water if it occurs. Store away from direct sunlight. Safe for fish, coral and invertebrates when dosed at the recommended rate.
Goes well with
- Red Sea Reef Care KH/Alkalinity Foundation B — magnesium is what lets this hold its level once dialled in.
- Red Sea Reef Care Calcium+ Foundation A — the calcium half of the same three-part program.
- Red Sea Reef Foundation Pro Multi Testing Kit — for tracking Mg alongside Ca and KH.
- Red Sea Reef Care Magnesium Foundation C (Powder) — same element, concentrated dry format, cheaper per litre on larger systems.
Warranty and delivery
Covered by the manufacturer's standard consumer guarantees in addition to your rights under Australian Consumer Law. Standard parcel delivery Australia-wide.
Common questions
Why won't my calcium and alkalinity stay balanced even though I dose them carefully?
Check magnesium first. Low Mg lets calcium and carbonate react and precipitate out of solution, which shows up as both Ca and KH refusing to hold — correcting magnesium is often what fixes it.
How fast can I raise magnesium?
Slowly. Split any correction larger than about 20 ppm over several days rather than dosing it in one go.
What's the difference between the liquid and the powder?
Both replenish the same magnesium blend. The liquid is ready to dose; the powder is mixed with RO/DI water into a stock solution and works out cheaper per litre on larger systems.
Will this affect my calcium or KH readings?
Not directly, but keeping magnesium in range is part of what keeps calcium and alkalinity dosing predictable — test all three together.
