Foundation B KH/Alkalinity 5L — Bulk Size for Large Reef Tanks - Red Sea

Foundation B KH/Alkalinity 5L from Red Sea is the complex of carbonate and seawater buffers in a 5 litre jug. Built for large reef tanks and dosing pumps that run daily — and alkalinity is almost always the element dosed most heavily.

Who the 5 litre is for

On a well-stocked SPS tank, the daily alkalinity dose is often counted in tens of millilitres. At that rate a 500ml bottle lasts weeks. The 5L jug cuts the refills, avoids running out mid-week, and costs less per litre.

If your tank is small or you are starting out, the 5L is oversized — see the smaller sizes below.

What alkalinity actually measures

Alkalinity is not "the carbonate level": it measures every buffering substance in the water — bicarbonate (HCO₃), carbonate (CO₃), hydroxide (OH) and borate (BO₃). Red Sea advises avoiding test kits that measure carbonates only, as they distort dosing calculations. Useful conversion: dKH = meq/l × 2.8.

Specifications

• Composition: carbonate and other seawater buffers
• Concentration: 1ml raises alkalinity in 100 litres (25 gal) by 0.036 meq/l (0.1 dKH) — identical to the other liquid sizes
• Daily maximum: 0.5 meq/l, or 1.4 dKH per day
• Sizes: 250ml, 500ml, 1L, 5L (this listing) and 1kg powder
• Suitable for: SPS, LPS and soft coral reef tanks · dosing pump compatible

⚠️ The powder version is not the same strength: 1g raises alkalinity in 100 litres by 0.12 meq/l (0.33 dKH). Never carry a calculation from one format to the other.

Target levels for your reef tank

An SPS dominant tank targets LOWER alkalinity (8.0 dKH) than a mixed reef (11.5): when nutrients are dropped for colour, lower balanced levels stress the corals less.

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: alkalinity 0.5 meq/l (1.4 dKH), calcium 20ppm, 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.

Common trap: adding buffer to a tank whose calcium is already at saturation causes precipitation and drops the calcium.

Need a smaller size?

For a mid-sized tank, the 1L. For a nano or to start out, the 500ml. Same liquid, same concentration.

Goes well with

Alkalinity that refuses to hold often traces to low magnesium — check with Foundation C Magnesium 5L. And buffer builds nothing without calcium: Foundation A Calcium+ 5L completes the trio.

Frequently asked questions

Is the 5L stronger than the 500ml?

No. Every liquid size has the same concentration: 1ml raises alkalinity in 100 litres by 0.1 dKH. Only the powder differs.

My alkalinity keeps dropping — why?

Red Sea lists three causes: new aragonite substrate, an unbalanced salt mix with low magnesium or high calcium, and excessive calcium dosing without magnesium. Test magnesium first.

How much can I raise alkalinity in one day?

By 0.5 meq/l at most, which is 1.4 dKH.

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.