Foundation A Calcium+ 5L — Bulk Size for Large Reef Aquariums - Red Sea

Foundation A Calcium+ 5L from Red Sea is the same product as the smaller bottles in a 5 litre jug: calcium, strontium and barium in the ratios of coral skeleton. Built for large reef tanks and for dosing pumps that run every day.

Who the 5 litre is for

A tank consuming 30ml a day empties a 500ml bottle in under three weeks. From that rate up, the 5L jug stops being a luxury: fewer refills, fewer mid-week run-outs, and a lower cost per litre.

It also fits dosing pump reservoirs — fill it and forget it for weeks. If your saltwater tank is under 200 litres or you are just starting, the 5L is oversized; see the smaller sizes below.

Why strontium and barium matter

A coral builds roughly 90% of its skeleton by combining calcium and carbonate into aragonite. The rest comes from magnesite, strontianite and other minor minerals. When magnesium or strontium run low, the skeleton forms with more calcite — more brittle. That is why Red Sea does not sell a plain calcium solution.

Specifications

• Elements: calcium, strontium and barium
• Concentration: 1ml raises calcium in 100 litres (25 gal) by 2ppm — identical to the other liquid sizes
• Daily maximum: 20ppm of calcium per day
• Sizes: 250ml, 500ml, 1L, 5L (this listing) and 1kg powder
• Suitable for: SPS, LPS and soft coral reef tanks · dosing pump compatible

Target levels for your reef tank

How to dose: the manufacturer's method

1. Bring Ca, Alk and Mg to their targets.
2. Run 4 days without dosing anything, topping up evaporation with fresh water.
3. Test, work out the dose to return to target, add it.
4. Divide by 4: that is your daily dose for the week.
5. Retest weekly and adjust.

Three rules not to skip

• Daily maximums: calcium 20ppm, alkalinity 0.5 meq/l (1.4 dKH), magnesium 10ppm.
• Dosing order: magnesium, then alkalinity, then calcium — 10 minutes between each. With three dosing pumps, stagger the schedules.
• Where to add it: into the sump, or slowly into a high-flow area.

Adding calcium to saturation levels causes a sudden drop in alkalinity.

Need a smaller size?

For a mid-sized tank, the 1L lasts months. For a nano or a trial, the 500ml. The contents are identical across all three — only the quantity changes.

Goes well with

A tank big enough for 5L of calcium burns through the rest too: Foundation B KH/Alkalinity 5L and Foundation C Magnesium 5L complete the trio in the same size.

Frequently asked questions

Is the 5L stronger than the 500ml?

No. It is the same liquid: 1ml raises calcium in 100 litres by 2ppm in every liquid size. Only the container changes. The powder version has its own concentration.

At what tank size does the 5L make sense?

Red Sea sets no threshold. In practice consumption decides: if your calculated daily dose passes roughly 20ml, a 500ml bottle is gone in under a month.

How much calcium can I add in one day?

20ppm at most, per Red Sea. Larger gaps are spread over several days.

Why buy from ReefSolution

Aquarium ReefSolution is an authorized Red Sea dealer. Our team works in marine aquariums in Laval and knows the Reef Care Program from real tanks. We ship across Canada and offer in-store pickup.