Reef Aquarium Basics
Reef aquarium fundamentals: target water parameters, lighting and flow needs, and an overview of soft, LPS and SPS corals.
What a reef aquarium is
A reef aquarium is a marine system that keeps living corals and other invertebrates alongside fish, recreating part of a coral reef. Corals and the reef community are sensitive to water chemistry, so a reef tank demands tighter parameter control than a fish-only marine tank. Many corals rely on symbiotic algae for energy, which is why light, flow and stable water chemistry all matter together rather than in isolation.
Target water parameters
- Salinity: 1.022-1.025 specific gravity (30-34 ppt)
- Temperature: about 24-27 °C (76-80 °F)
- pH: 8.2-8.6
- Alkalinity: 7-12 dKH
- Calcium: 400-450 ppm
- Nitrate: 0-10 ppm; phosphate: 0-0.06 ppm; ammonia and nitrite: 0 ppm
Lighting
Lighting needs depend on the corals kept. Some corals, such as mushroom and polyp corals, require relatively little light, while small polyp stony corals such as Acropora and Montipora need high-intensity lighting to support their symbiotic algae.
Water flow
Reef tanks rely on strong, varied flow to deliver food and oxygen to corals and to carry away waste. A common general guideline is a turnover of around ten times the tank volume per hour, with adjustments for the specific corals being kept.
Coral types
Corals are broadly grouped into soft corals, large polyp stony (LPS) corals and small polyp stony (SPS) corals. Soft and mushroom corals tend to be more tolerant of variable conditions, while SPS corals such as Acropora are the most demanding of light, flow and stable chemistry.
Filtration
Biological filtration in a reef tank is provided mainly by live rock populated with beneficial bacteria, which are pieces of rock and sand broken from the reef and colonised by these organisms. A protein skimmer is commonly used to remove dissolved organic compounds by foam fractionation, a process in which air is introduced into a water stream to create microbubbles that carry waste out before it breaks down. While some sources cite a target of 24-27 degrees Celsius (76-80 Fahrenheit), reef tanks are also commonly kept between 25 and 28 degrees Celsius (77 and 82 Fahrenheit) as long as the temperature is held stable.