Seachem Reef Builder
Cost per litre
Under 1c
Water type
Marine + Reef
Seachem Reef Builder
Raises alkalinity without the pH jolt. Seachem Reef Builder is a phosphate- and organic-free carbonate supplement that lifts and holds alkalinity in the reef aquarium without immediately shifting pH — and unlike a straight pH buffer, it won't deplete calcium, magnesium or strontium as it works.
Key features
- Raises carbonate alkalinity (KH) without an immediate pH swing.
- Won't deplete calcium, magnesium or strontium the way some straight buffers can.
- Phosphate- and organic-free — won't feed nuisance algae.
- Scales to a dosing pump — a continuous-drip dosing formula is published for automated systems.
- Costs under 1c per litre of tank water dosed at every pack size.
Specifications
| Pack size | Price | Standard dose | Litres this pack doses |
|---|---|---|---|
| 300 g | $28.95 | 3 g per 150 L, twice weekly | 15,000 L |
| 600 g | $48.95 | 3 g per 150 L, twice weekly | 30,000 L |
| 1.2 kg | $89.95 | 3 g per 150 L, twice weekly | 60,000 L |
| 4 kg | $268.95 | 3 g per 150 L, twice weekly | 199,950 L |
Suitable for, and not suitable for
- Suitable for reef and marine aquariums that need steady carbonate alkalinity without a pH spike — a good fit for dosing pumps and continuous-drip setups.
- Not a calcium, magnesium or strontium source on its own — pair it with a calcium supplement such as Reef Complete.
- Not for freshwater aquariums.
Dosage and directions
Beginner dose: dissolve 3 g (½ level teaspoon) in at least 250 mL of freshwater and add per 150 L of system volume, twice weekly. Check alkalinity every fortnight and adjust from there. Each 3 g/150 L dose raises alkalinity by roughly 0.25 meq/L; do not exceed 12 g per 150 L in a single day.
For a continuous dosing pump, Seachem publishes the formula m = 0.08 × v × a, where m is grams of Reef Builder, v is tank volume in litres and a is the meq/L rise wanted — for example, roughly 16 g dosed into top-off water lifts a 200 L system by 1 meq/L.
Cost per litre at every pack size works out under 1c, calculated on the standard dose:
| Pack size | Cost per litre dosed |
|---|---|
| 300 g | Under 1c per litre |
| 600 g | Under 1c per litre |
| 1.2 kg | Under 1c per litre |
| 4 kg | Under 1c per litre |
Safety
- Do not mix directly with a calcium, magnesium or strontium supplement — dose on alternate days or space doses at least 30 minutes apart.
- Do not exceed 12 g per 150 L per day. Excess alkalinity can still push calcium, magnesium and strontium out of solution even though Reef Builder is gentler on pH than a straight buffer.
- A Safety Data Sheet is available from Seachem for handling and storage guidance.
Care and storage
Keep the container sealed between doses and store somewhere dry — moisture will cake the powder.
Goes well with
- Seachem Reef Complete — the calcium, magnesium and strontium side of reef chemistry.
- Seachem Reef Buffer — where pH also needs correcting, not just alkalinity.
Warranty and delivery
Covered by the manufacturer's standard warranty against defects, in addition to your rights under Australian Consumer Law. Standard freight.
Common questions
What's the difference between Reef Builder and Reef Buffer?
Reef Builder raises alkalinity without an immediate pH shift, which suits systems where pH is already fine and only alkalinity needs topping up. Reef Buffer moves pH toward 8.3 at the same time it raises alkalinity.
Can I run this through a dosing pump?
Yes — Seachem publishes a continuous-drip dosing formula (m = 0.08va) for exactly this. Mix a stock solution and dial in the daily volume to your target alkalinity rise.
Will it crash my calcium?
Overdosing alkalinity relative to calcium can still pull calcium out of solution, so keep to the maximum dose and test regularly rather than dosing on a fixed schedule alone.
How is this different from a liquid alkalinity supplement?
Reef Builder is a powder, which is generally the cheaper way to buy alkalinity in bulk. Seachem Reef Carbonate is the liquid equivalent, better suited to dosing pumps that can't handle powder.
