• Calcium and strontium in seawater ratio — replenishes what stony corals consume building skeleton.
• Concentrated liquid — 1 mL per 100 L raises calcium by about 2 ppm; no mixing required, dose straight from the bottle.
• Designed to be dosed alongside Foundation B and C, in that ratio, for balanced reef chemistry rather than a calcium-only fix.
• Three sizes — 500 mL, 1 L and 5 L, for hand-dosing through to automated systems.
• Works with a Red Sea Reef Foundation test kit to set the dose from your own measured calcium uptake.

1 mL per 100 L raises calcium by approximately 2 ppm. Red Sea's published starting rates by reef type:

Don't raise calcium by more than 20 ppm in a day — spread larger corrections over several days. When dosing Foundation A, B and C manually together, add magnesium first, then alkalinity, then calcium, about 10 minutes apart, to avoid a local spike that can cloud the water or precipitate elements out of solution.

As a worked example only: a 300 L mixed reef dosed at the ~3 mL per 100 L per day guide rate uses about 9 mL a day — a 1 L bottle would last roughly 110 days at that rate. Actual use depends entirely on your coral load and test results, which is why we haven't set a fixed cost-per-litre figure on this page.

One bottle of Foundation A (Calcium+) concentrate, in the size selected. Foundation B (Alkalinity) and Foundation C (Magnesium) are sold separately and are needed alongside it to run the full three-part programme.

Suitable for saltwater reef aquariums running stony or soft coral, clams or coralline algae, where calcium needs topping up against consumption.

Not suitable for fish-only systems with no calcium demand, and not a substitute for testing — dosing calcium without checking alkalinity and magnesium alongside it can throw the three out of balance.

Covered by the standard manufacturer guarantee against faulty product, in addition to your rights under Australian Consumer Law. The 5 L size ships as a heavier parcel; standard delivery otherwise.

Do I need Foundation B and C as well?

Yes, for balanced chemistry — dosing calcium alone without alkalinity and magnesium keeping pace can push the three out of the ratio corals need, even if calcium itself reads fine.

How much will this raise my calcium?

1 mL per 100 L raises calcium by about 2 ppm as a stock-solution figure — test before and after a few days of dosing to see your reef's actual response, since coral uptake affects the net change.

Which size should I buy?

500 mL and 1 L suit hand-dosing on smaller reefs; the 5 L size costs less per mL and suits larger systems or a dosing pump reservoir you don't want to refill often.

Can I dose all three Foundation parts at the same time?

Not at exactly the same moment — Red Sea recommends about 10 minutes between magnesium, alkalinity and calcium when dosing manually, to avoid a local concentration spike.

Is this the same as the RCP 4-Part kits you sell?

Related but not identical — the RCP kits bundle Foundation A and B together with the two Colours trace-element bottles at a fixed reef-volume ratio. Foundation A on its own lets you buy calcium separately if your alkalinity or magnesium consumption differs from the standard ratio.