Brightwell Aquatics Reef Code A Calcium Supplement, 500 mL for Reef Aquariums

Brightwell Aquatics Reef Code A is a 500 mL calcium supplement for aquariums, designed as the calcium half of a two-part calcium-and-alkalinity dosing system used with equal parts Reef Code B.

• Paired in equal parts with Reef Code B — provides a two-part dosing approach designed around natural seawater ratios.
• Contains calcium, magnesium, strontium, potassium, and minor and trace minerals — supplies a range of minerals for reef aquarium water.
• Designed for corals, clams, and calcareous algae — supports reef-building organisms while simplifying calcium and alkalinity maintenance.
• Contains no phosphate, silicate, or organic material — avoids adding these substances through the supplement.
• Formulated by a marine scientist and made in the USA — brings its stated formulation origin and manufacturing origin into focus.
• Brightwell Aquatics describes the formula as stronger than most competing products — a stated differentiator for reef keepers comparing calcium supplements.

Maintaining calcium and alkalinity is part of caring for reef aquariums with organisms that build calcium-based structures. Reef Code A is intended for new aquarium setups as well as established tanks, and the brand also identifies its aquarium water treatments for freshwater and marine environments. For reef use, pair A with Reef Code B as a two-part system.

Which reef organisms is Reef Code A made to support?

Brightwell Aquatics Reef Code A is formulated to support reef-building organisms, including corals, clams, and calcareous algae. Its calcium supplement role is intended to help simplify the ongoing maintenance of aquarium calcium and alkalinity, rather than serving as a food for these organisms.

• Intended for reef-building organisms that use calcium.
• Made for aquarium water treatment and calcium maintenance.

How does the Reef Code A and B method work?

Brightwell Aquatics Reef Code A supplies the calcium component, while Reef Code B provides carbonates and other anions; use equal parts of each. Together, the two-part method is designed to maintain ionic balance in proportions that reflect natural seawater. Reef Code A also contains magnesium, strontium, potassium, and minor and trace minerals. The formula contains no phosphate, silicate, or organic material.

• Reef Code B is the companion part for the two-part method.
• Equal-part use is the stated approach for matching the natural seawater ratio.

How much should I dose, and how do I prepare it?

Brightwell Aquatics Reef Code A directions call for 5 mL per 25 gallons (94.6 L) of water every other day, or as needed to sustain alkalinity within 412 to 450 ppm. Shake the product well and test calcium concentration before dosing. When used as directed, 250 mL treats up to 1,250 gallons (4,732.5 L).

• Begin by testing calcium concentration before adding the supplement.
• Use the stated alkalinity range as the dosing target.

Can Reef Code A be used in freshwater and marine aquariums?

Brightwell Aquatics Reef Code A is identified for use in both freshwater and marine aquarium environments, while its calcium-and-alkalinity two-part method is presented for reef aquarium care. The product is intended for use with Reef Code B as part of that method. It is suitable for setting up a new tank or maintaining an established aquarium.

• Made for aquarium water treatment in freshwater and marine settings.
• Reef dosing uses Reef Code A together with Reef Code B.

Reef keepers maintaining calcium and alkalinity for corals, clams, or calcareous algae will get the most direct use from Reef Code A. It fits aquarium owners looking for a two-part dosing routine with a dedicated calcium component.

Read our guide: A beginner’s aquarium set-up checklist: from bowl to tank