How to Grow Coralline Algae in a Saltwater Aquarium

Pink Coralline algae on aquarium glass

 FalsePerc / Wikimedia Commons / CC by 3.0

Encrusting coralline algae growth gives many saltwater aquariums a pinkish-red color, and most marine aquarists aim for a good covering of the algae. Although coralline algae comes in many different colors—there are more than 1,600 species—it's usually thought of as pink, red, purple, or some shade in the same color family.

Unlike brown, green hair, and red slime algae, all of which frequently grow in an aquarium whether you like it or not, coralline algae must be physically brought into the aquarium for it to reproduce and populate the various surfaces.

Coralline algae can be introduced into your aquarium by adding:

  • Coralline-covered live rock
  • Coralline scrapings from another aquarium
  • Commercial coralline algae starter packages

The more species of coralline algae that you add to your aquarium, the more you will see growing on your live rock, substrate and aquarium walls. An advantage of growing coralline algae is that it out-competes the growth of nuisance algae like hair algae, green algae, diatoms, and mat algae (in a normal reef environment with proper water chemistry). Coralline algae grows on live rock where nuisance algae might otherwise grow.

Once you have some coralline algae growth in your aquarium, let it grow and spread by briefly turning off all external filters and skimmers, leaving any powerheads running. With a single-edged razor blade, scrape some of the existing coralline algae off the front and side tank walls. The water current generated by the powerhead will spread the coralline scrapings throughout the tank where they will continue to grow. After an hour or so, turn the skimmers and filters back on.

Coralline Algae Lighting

As with other forms of algae, coralline algae requires light. Exactly how much or little light is required for optimum growth varies with the types of coralline algae. Some prefer higher lighting, while others prefer low lighting. Aquarists have found that as their tank lights get older and the spectrum and intensity fades, their coralline algae growth increases. However, these growths died off in the well-lit areas and increase in the lower lit and shaded areas of the tank when the lights were replaced.

What type of lighting is best? There is no single answer. Some types of coralline algae will grow better under certain lighting, while other types will grow better under different lighting. For the most part, it seems that coralline will grow under minimal reef type lighting. 

Coralline algae up-close
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Coralline Algae Water Chemistry

While lighting is important, maintaining excellent water quality might be the biggest factor in growing a good crop of coralline algae. Like hard corals, coralline algae growth is calcareous by nature, requiring many of the same things coral does to flourish:

  • water Specific Gravity around 1.024
  • Calcium: 350 to 480 ppm
  • Carbonate alkalinity: between 2.5 and 4.0 meq/L (7-12 dKH)
  • Strontium in the water
  • Low phosphate (Close to 0)
  • Low nitrate (5 ppm or lower)

Many aquarists have found that performing regular water changes will keep the phosphate and nitrate levels in check, as well as keeping the calcium, alkalinity, and strontium at or near optimum levels. Using mangroves can also be a simple and inexpensive method for reducing nitrate and phosphate, and using calcium and strontium additives produces the same or better results without the constant expense of sea salts and RO/DI water required for water changes. Additionally, many aquarists have also found that using a good protein skimmer goes a long ways towards controlling nitrate and phosphate. 

Tank algae
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Causes of Disappearing Coralline Algae

Once they have established a healthy coralline algae population in the aquarium, many aquarists are puzzled by what appears to be a constant reduction in their coralline algae colonies. If the water quality is being kept at the optimum level, what could be the cause? Some possibilities are:

Spending some time watching your tank critters at work will reveal which of them is attacking your coralline algae growth. As long as the coralline algae is growing faster than the critters are consuming it, you will be providing food for them and maintaining a healthy aquarium.

Algae up-close
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