Seachem Reef Builder

Seachem Reef Builder is a dry blend of carbonate salts that raises carbonate alkalinity (KH) in a reef aquarium without immediately changing pH. Alkalinity is what keeps your pH stable and gives stony corals and coralline algae the carbonate they need to build skeleton, so when it drifts low your whole tank gets harder to keep steady. Reef Builder restores it cleanly, and with long term use it gently tends to stabilize pH around 8.3. Browse our full range of reef additives and supplements and the rest of the Seachem lineup.

Why Reefers Use It

• Raises KH, not pH. Restores carbonate alkalinity without the pH spike, so you can correct alkalinity even when your pH is already where you want it.
• Protects the rest of your chemistry. Used as directed it will not deplete calcium, magnesium, or strontium, which often precipitate out when alkalinity is pushed up carelessly.
• Stabilizes over time. With ongoing use pH tends to settle and hold near the natural reef target of 8.3.
• Pairs with Reef Buffer. Use the two together to dial in both alkalinity and pH independently.

How to Use

Dissolve 3 g (about 1/2 level teaspoon) in at least 250 mL of fresh water, then add it to the tank for every 150 L (40 US gallons), twice a week or as needed to hold your numbers in range. Each 3 g per 150 L raises alkalinity by roughly 0.25 meq/L (about 0.7 dKH). Do not exceed 12 g per 150 L in a single day. Keep reef alkalinity in the 3 to 5 meq/L (8 to 14 dKH) range and never let it fall below 2 meq/L.

Important: do not directly mix Reef Builder with any calcium, magnesium, or strontium supplement. Add your alkalinity and calcium products on alternate days, or at least 30 minutes apart, so they do not react in the water column.

Reef Builder or Reef Buffer?

They sound alike but do different jobs. Reef Builder raises carbonate alkalinity without affecting pH. Reef Buffer raises carbonate alkalinity and pH together, toward 8.3. Reach for Reef Builder when your pH is already on target and you just need to bring KH up. Reach for Reef Buffer when your pH is running low. The two can be used in the same system.

Choose Your Size

Each dose is 3 g treating 150 L (40 US gallons). Actual usage depends on your tank's alkalinity demand.

Specifications

Recommended Pairings

• Seachem Reef Advantage Calcium for the calcium side of the balance.
• Seachem Reef Advantage Magnesium to keep calcium and alkalinity holding where you set them.
• Seachem Reef Buffer when you need to raise pH along with alkalinity.
• A reliable alkalinity test kit so you are always dosing to a real number.

FAQ

What does Reef Builder actually do?
It raises carbonate alkalinity (KH) in a marine tank without immediately changing pH, giving corals and coralline algae the carbonate they need while keeping pH steady.

Will it raise my pH?
Not right away. Reef Builder is designed to lift alkalinity on its own, and with continued use pH tends to settle near 8.3. If you specifically need to bring pH up, use Reef Buffer instead or alongside it.

Can I dose it at the same time as my calcium supplement?
No. Do not directly mix it with calcium, magnesium, or strontium products. Dose them on alternate days, or at least 30 minutes apart.

How much will one dose move my alkalinity?
Roughly 0.25 meq/L (about 0.7 dKH) per 3 g in 150 L (40 gallons). Always test and adjust toward the 3 to 5 meq/L target.

Can I use it in freshwater?
No. Reef Builder is formulated for marine and reef aquariums only.