Coralline algae title image

Coralline algae–the algae you want in your tank

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.

coralline algae


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 on glass
Perhaps the only downside to growing coralline algae in your tank is that you may need to clean it off the glass


Coralline algae are attractive and are a sign of a healthy aquarium. Do you have coralline algae growing well in your tank?

Show it off. Post it on Pinterest and link to it here, I want to see it!






7 responses to “Coralline algae–the algae you want in your tank”

  1. Paul saunders

    Hi Al,
    I added a blue tuxedo urchin a few months back and I’ve noticed a huge reduction in my coralline algae now, as he eats it quicker than my tank produces it. I’ve been considering removing the urchin as i do like a fairly heavy purple coralline like I used to have. He also dislodges a lot of my frags. But urchins also eat a lot of nuisance algae, which other than glass dusting and small sand brown patches, I don’t see any of.
    What would your thoughts/recommendations be?
    Pros vs cons? Keep vs remove urchin?

    1. Hi Paul, thanks for the comment. I have an opinion (of course) but not a lot to add to your note. Your experience with a tuxedo urchin is exactly the same as mine. They ate good and bad algae–and left a trail of destruction behind them. I lost frags b/c I wasn’t paying attention–the corals died from damage/being upside down in the sand for days before I noticed and/or fixed. So those, in my mind are the pros/cons. My choice was to remove but of course it’s up to you–if you love the urchin enough. Great comment-thank you for adding your experience here–it hadn’t occurred to me to go deep on urchins here.


      1. Paul saunders

        Thanks for replying Al.
        You’ve just confirmed my own thoughts, I was waiting to see if you had any other pros to add to keeping an urchin.
        I think it’s time for him to move out. I also have a porcelain crab now too as originally I had a few spots of bubble algae. He can keep keep an eye out for any other algae and I can get my coralline back.

  2. Dennis

    Hey Al
    Coralline algae is truly the canary in the coal mine of a reef tank. Whenever in the past I have had a die back in the coralline algae, I started to look for parameter problems. You know how it happens. Everything in the tank is growing well the coralline algae is jamming pumps, protein skimmers, sumps, it is just everywhere. You start complaining about it, your wife asks you about it constantly. I tell her I will clean it this weekend, but I secretly don’t. I have become complacent. You see the aforementioned growth has given me the “reef expert head”. I can make a reef grow so well I betcha I can grow one in my mother-in-laws hairdo. But then murphy’s law kicks in, and my neglect and my makes the tank take a downturn. The coralline algae take downturn and recedes, and my stony corals follow suit. I follow with full blown panic. My neglect turns into over care and I make it worse. To top it off my wife constantly tells me about how my corals don’t look as good as they used to. I resign to the fact that a “reef tank expert” has never applied to me. It is a humbling experience. You know the weird thing about this is that I have had the experience more than once. Just wondering if anyone else has. It seems lonely sometimes. Love the blog Al.

    1. Dennis,

      Thanks for the comment. Canaries they are–it is a fitting analogy. As far as not cleaning it regularly…the images here are of the front right corner of my tank. it’s really hard to reach…and I use the same excuses you do…I’ll get to it this weekend…For what it’s worth, your description of being ‘on top of it’ then falling off then bouncing back also describes my behavioral cadence. In fact, that’s what prompted me to do the 31 day challenge back in March–to try and jump start. I think there are some that are able to maintain that consistency but some of us (myself included) are cyclical. The key is to try and recognize the first signs the canaries aren’t happy and use that as enough impetus to get back in the game. I’m curious to see what others think

  3. Jim Bowden

    Hi Al;

    I believe I have coralline algae growing plentiful on one side of my Aquarium wall. So I’ll let you confirm that for sure and let me know for sure! Had a problem attaching my photo on the pin interest link you provided, so will forward that photo under separate email to you. Thanks.


    1. Jim, great to hear from you again, sir. Sorry about the trouble pinning. That was a new experiment here. Kudos on the healthy tank!

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