Algae Is Killing Corals in an Aquarium

The bane of reef aquarists everywhere, algae crops up whenever tank conditions deteriorate. These fast-growing nuisances invade bare rock surfaces and compete with coral for space, light and scarce nutrients. Excess nitrogen and phosphorus nutrients fuel prolific, rapid algae growth. These nutrients enter the tank's ecosystem as fish food but quickly dissolve and change composition, becoming available to all the tank's inhabitants, including algae. The solution to any algae problem lies with the aquarist's skill, knowledge and ability to remove the excess nutrients from the tank. Buying crabs, snails or algae-eating fish only speeds up the tank's nutrient cycles and ultimately solves nothing.

  1. Change the Lights

    • As fluorescent and metal halide lamps age, their color spectrum shifts. Reef-specific lamps initially favor blue and white light, replicating a coral's experience in shallow water reefs. Over time, repeated on/off cycles degrade this color and shift the light to red and yellow wavelengths. Algae grow rapidly under red and yellow light, taking full advantage of any excess nutrients present in the water column. Changing old, degraded lights for new lights inhibits algae growth and gives an aquarist additional time to bring down nitrogen and phosphorus levels.

    Increase the Flow

    • Intense, dynamic water flow on a reef keeps the entire ecosystem moving constantly. Mimicking the reef's powerful water currents in a captive system keeps food and waste from settling and decomposing in quiet corners and crevasses. Decomposition releases large amounts of stored nitrogen and phosphorus and drives algae growth. Add external pumps or powerheads (small and powerful in-tank pumps) to eliminate dead spots and increase the overall water flow. Good water currents keep food and waste suspended in the water long enough to be eaten or caught by the filter.

    Upgrade the Filtration

    • Ultimately, algae growth ceases when nutrient removal equals or exceeds nutrient input. Numerous methods for filtering the water exist. Protein skimmers are one of the best. These specialized filters utilize the surface area of millions of tiny air bubbles mixing with water to pull dissolved waste out of the tank. Think of a balloon attracting hundreds of pieces of dust to its surface and then discarding the balloon: that's the general idea behind a protein skimmer. Many aquarists maintain two protein skimmers because different designs remove different dissolved compounds. Other effective filters include sock filters which trap microscopic detritus, traditional mechanical filters with replaceable cartridges, activated charcoal pellets designed to soak up waste at a molecular level, and deep sand beds, where trillions of bacteria modify nitrogenous waste until the nitrogen bubbles out of the tank as gas.

    Change the Water

    • The traditional water change remains the best long-term tool for maintaining a reef tank and managing algae. Filtration simply cannot remove all waste compounds. These unwanted chemicals only leave the tank by draining old saltwater. Aside from bulk nitrogen and phosphorus removal, a water change refreshes the water quality by reintroducing many minor ions needed by coral physiology. Good tank maintenance includes changing at least 20-30 percent of the water each month. Manually removing nuisance algae while performing a water change exports even greater amounts of waste: the algae locks up nitrogen and phosphorus in its cellular matrix.

    Change Takes Time

    • Algae problems never clear up overnight. Even after changing the lights, revamping the flow, upgrading the filtration and performing a water change or two, eliminating nuisance algae takes time. Pockets of phosphorus remain buried in sand, coral needs time to rebound and algae releases nitrogen while slowly withering away. A month or two of diligence and patience rewards an owner with a clean tank and thriving coral. Remember the aquarists' axiom, "nothing good ever happens fast in a reef tank."