Reef Builder — KH Alkalinity Without Immediate pH Impact 600 g and 1.2 kg - Seachem

Seachem Reef Builder is a powdered alkalinity supplement that increases carbonate hardness (KH) with minimal and gradual impact on pH. With long-term use, the pH stabilizes at 8.3. Its blend of carbonate sources does not deplete calcium, magnesium, or strontium, unlike competing products based solely on sodium bicarbonate. Available in 600 g and 1.2 kg — the larger size is the economical choice for aquarists who regularly dose alkalinity or use a dosing pump.

Main advantages

• Increases carbonate alkalinity (KH) without immediately affecting pH
• Blend of carbonate sources — does not lower pH like bicarbonate-only products
• Does not deplete calcium, magnesium, or strontium
• Economical 1.2 kg format for regular and automated dosing
• Compatible with pre-mixed solution dosing pumps

Use in reef aquariums

Carbonate alkalinity is essential for the growth of all corals. Seachem recommends maintaining alkalinity between 3 and 5 meq/L (8–14 dKH), never dropping below 2 meq/L. Reef Builder and Seachem Reef Buffer can be used together: Reef Builder to increase alkalinity without changing pH, Reef Buffer to increase both alkalinity and pH simultaneously. When pH is not a concern, Reef Builder is the first choice for adjusting alkalinity.

Dosage

• Beginner: 3 g (½ level teaspoon) per 150 L (40 US gallons), twice a week. Dissolve in at least 250 ml (1 cup) of fresh water. Check alkalinity every 2 weeks.
• Advanced: dose until alkalinity reaches 3–6 meq/L (8–17 dKH). Each 3 g dose per 150 L raises alkalinity by 0.25 meq/L. Do not exceed 12 g per 150 L per day.
• Expert: determine the consumption rate and set up a continuous drip. Formula: m = 0.08 × v × a (m = grams, v = volume in liters, a = increase in meq/L).

Preparing for a dosing pump

According to Seachem, 1 teaspoon of Reef Builder dissolves in 150 ml of liquid, which is 33.3 g per liter of RO/DI water. The 1.2 kg size makes over 35 liters of concentrated solution. It is normal for the pre-mixed solution to be slightly cloudy — add it to the tank after a few minutes of rest. Small amounts of calcium carbonate may form if the solution sits for a long time, but they dissolve in the aquarium volume.

Manufacturer's precautions

• Do not exceed 12 g per 150 L per day
• Excess alkalinity can accelerate the loss of calcium, magnesium, and strontium
• Do not mix directly with a calcium, magnesium, or strontium supplement — alternate days or wait at least 30 minutes

Available formats

• 600 g
• 1.2 kg

Why choose Reef Builder at ReefSolution

The 600 g covers the needs of a typical reef tank; the 1.2 kg is ideal for aquarists who go through alkalinity regularly, especially SPS tanks with dosing pumps. Pair Reef Builder with Reef Advantage Calcium for calcium and Reef Buffer if pH also needs correcting. The equivalent liquid version is Reef Carbonate, and for two-bottle calcium + alkalinity dosing, Reef Fusion 2 is the alkalinity half of Seachem's two-part system. Monitor your parameters with a reliable alkalinity test kit.

Frequently Asked Questions

Is the 1.2 kg size worthwhile for automated dosing?

Yes. The 1.2 kg size makes more than 35 liters of concentrated dosing-pump solution (33.3 g per liter of RO/DI water). Ideal for systems with high alkalinity consumption and daily dosing.

What is the difference between Reef Builder and Reef Carbonate?

Reef Builder is the powder version, while Reef Carbonate (4000 meq/L) is the liquid version. Both give the same end result. Powder is more economical for large volumes; liquid is easier to dose without pre-mixing.

Does Reef Builder affect aquarium pH?

Not immediately. Reef Builder raises alkalinity with minimal pH impact. With long-term use, pH tends to stabilize at 8.3. To raise pH right away, use Seachem Reef Buffer.