Corals Gone Wild: Don’t Let Encrusting Polyps Take Over Your Tank!

Green Star Polyps can grow rapidly and encrust live rock, other corals, substrate, aquarium walls, and more.

Green Star Polyps can grow rapidly and encrust live rock, other corals, substrate, aquarium walls, and more.

I have a confession to make. When I mention my 75-gallon “reef tank” in my posts here at Saltwater Smarts, I’m not being entirely truthful in my terminology.

When I first set up the tank almost 14 years ago and over many of the ensuing years, it could accurately be described as a reef system. It contained a nice mix of soft corals and a few large-polyp stony corals to boot.

Today, a better descriptor for the tank might be “Green Star Polyp Paradise” or perhaps “The Green, Green Polyps of Home.” Why? Through my own benign neglect, approximately two-thirds of the tank has now become completely overrun with green star polyps.

Most of the rocks are smothered with the stuff, and the only corals that haven’t yet succumbed to the “Creeping Green Menace” are a gorgonian (though the star polyps are doing their level best to gain a purchase on it), a finger leather coral located at the far left-hand side of the tank, and an open brain coral situated toward the front right-hand side of the tank and more or less out of reach of the star polyps (for the moment).

Oh, and did I mention much of the tank’s back pane is covered with pulsing Xenia? Yep, I let that get away from me, too.

With so much real estate dominated by the star polyps and pulse corals, the aquascape in the system just isn’t all that appealing to me anymore. I want a variety of interesting corals to enjoy—not a monochromatic, monospecific mess. But, alas, there it is!

Salty citizens, hear me out! This could happen to you! (And if you can identify the origin of that saying, you’re at least as old and nerdy as I am.) However, it’s not a foregone conclusion if you take the following steps to keep rapid-spreading, encrusting corals (star polyps, pulsing Xenia, colonial zoanthids, and the like) in check:

Exclude ‘em

Pulsing Xenia is a fast-growing coral species.

Pulsing Xenia is a fast-growing coral species.

Obviously, the best way to prevent fast-spreading corals from taking over your tank is to avoid introducing them in the first place. But keep in mind that knowing which species are apt to do this takes a bit of prior research, especially if you’re new to reefkeeping and buying your first corals. Don’t just purchase an assortment of nice-looking specimens and hope for the best.

Also, be aware that green star polyps and other fast-growing species are commonly (and justifiably) sold as part of “beginner coral packs” featured by various vendors. If you choose to purchase such an assemblage, be sure to verify all of the species in it and research their needs and growth habits.

Isolate ‘em

Green star polyps and other encrusting corals will rapidly grow onto any adjacent rocks, glass, acrylic, or other hard surfaces—in some cases, as mentioned above, even onto and over other coral species. To keep these corals from growing where you don’t want them, it’s helpful to position them at least several inches away from other rocks or corals. They’ll still spread outward from the rock they’re growing on and likely down onto the substrate, but it’s a lot easier to cut and detach them from loose substrate than from irregular-contoured rocks.

If the coral grows up onto the sides of the tank and you don’t want it there, the encrusting tissue/polyps can simply be scraped off with a razor blade (or an acrylic-friendly alternative)—which finally brings us to…

Propagate ‘em

Polyps or tissue mats pruned away from the larger colony or scraped off the glass/acrylic can usually be attached to small rocks or rubble (via rubber bands or aquarium-safe cyanoacrylate gel) with little difficulty. Or, you can place them loose in a rubble tray and wait for them to attach to pieces of rubble naturally. Your local aquarium store may be willing to take these frags off your hands in exchange for cash or store credit.

What’s your technique?
If you’ve got green star polyps or a similar weed-like coral in your tank, what’s your secret for keeping its growth in check? Let us know in the comment section below.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. I’m using a rose bubble tip anemone & a pulsing xenia to keep my green star polyp cornered. The xenia can only grow onto the substrate the entire rock is small enough to be lifted out of the tank so I can ‘trim’ easily into a safe bucket. This means I ‘get’ to have/risk keeping two spreading menaces in my smaller 40gallon set up without too much trouble. I’ve had both in their current location for over a year both do require regular ‘trimming’ but haven’t taken over 🙂

    • "Caribbean Chris" Aldrich says

      I love the “standoff” technique you’re using, Kate. Great thinking! For some reason it reminds me of the Old West, haha.

    • Karla Hazlewood says

      How do you “trim” it? My husband bought a rock with xenia on it. It spread well (to well) in his tank and when I set up my tank, I asked for a piece. It did NOT go well. The second biggest colony he had he gave me and immediately it went limp and refused to stand up or pulse. I moved the rock a couple of times and it still didnt do well. It didnt die tho. Then HIS spread all over his tank in tiny spots. SO he gave me his original large rock with the mother colony on it. It perked right up and turned pick and started to pulse. It is HUGE and beautiful. The first one he gave me changed colors. It is now almost lilac (the original is pink). But its now doing well. However, HIS tank is being over run. I want to clean his out of some of the xenia and put them in my spare (hospital) tanks, as we are planning on setting up a 75 gal in the living room soon. How do I get them off the rock without hurting them.

  2. Trimming and then using boiling saltwater from tank with my feeder tube to keep the edges of the intruding colonies in check.

  3. One word: isolation. I have wavy fingers xenia on one chunk of rock on substrate away from the rest of the tank. My local fish store guy was cool enough to warn me of its proliferation. I’ve had it a while with no problems. Looks nice and haven’t had to cut back at all. If you want xenia, it’s the only way. Don’t have experience with green star though. I think Kate’s technique seems pretty legit.

  4. I put my Green Star Polyps on a rock that only goes so far before it blocks the light. This keeps the star polyps from growing too far down the rock, and then i put that rock on top of another rock

  5. On Alameda beach, near San Francisco, I found green, red, and brown alge in the current. It looks like most of the same you would buy. Am I able to acclimated it to my refugium of my saltwater fish tank ?

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