I don’t think the average aquarium owner thinks about algae as being a good thing—but there are algae, Coralline Algae, that are desirable, attractive and a hallmark of a healthy tank.
Although the word coral is in coralline algae, they are certainly not corals. Coralline algae are macroalgae that has a calcified (stony) skeleton, similar in some ways to the skeletons of large polyp and small polyp stony corals.
Coralline algae come in a range of colors. Green coralline algae, red coralline algae, and purple coralline algae are the most common.
The most common varieties are encrusting—meaning they grow low and cover the rocks and glass, although a few of the more interesting and rare types are plating species that almost look like montipora corals. Very cool.
One the great things about the encrusting variety is that they will grow on the live rock and compete for the same space those problem algae might otherwise try to occupy, but in the game of musical chairs that is survival on a reef—whoever gets there first and grows fastest generally wins.
Where do Coralline algae come from?
Most times, coralline algae hitchhike their way into your tank on live rock and coral plugs. All you need is a small amount to seed your tank and with the proper growing conditions, your coralline algae will thrive.
Some people have suggested that you can spur additional growth of coralline algae on new rocks by scraping a small amount off of a rock and spreading it in the water flow. I’ve never done this deliberately except to scrape it off the aquarium glass (on which it obviously reached without any help from me). I’m not disputing that method, it seems to make some sense that it could help make an otherwise encrusting colony water-born and therefore more likely to settle somewhere else—but in my experience, this is not necessary.
New live rock often gets diatoms and cyanobacterial growth first—but once they die back, the surface of the rock will start to get light green, pink and even purple pigments—and then after some time and with sufficient calcium and pH, coralline algae.
Coralline algae will grow rapidly if water conditions are suitable. They need almost the same conditions as most stony corals: good pH (above 8), low nitrate levels and enough calcium (about 400 mg/l).
On the other hand, they will fade in the presence of nitrates, phosphates, and high CO2 levels.
You will soon notice your algae taking over most shady areas in the tank, quickly covering the aquarium glass, live rock, powerheads, and even some hermit crab or snail shells.
In a well-cycled tank the coralline will thrive in just a few months, covering most of your live rock substrate and even more.
Pros and cons
Let’s take a look at a few of the pros and cons of coralline algae in a saltwater aquarium:
- These algae take up the space that would be occupied by nuisance algae
- Are generally found to be attractive, on their own merit
- Are a canary in the coal mine, of sorts, serving as a yardstick on which to measure the health of the aquarium system (healthy coralline means a healthy tank)
- Don’t have any special requirements—just a healthy reef tank environment
- The only con I can think of is that they are sometimes a hassle to scrape off the aquarium glass. I have some significant growth in one corner of my aquarium that is hard for me to reach due to the depth and angle of the bow front glass.
- Um…that’s it.
Coralline algae are attractive and are a sign of a healthy aquarium. Do you have coralline algae growing well in your tank?
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