Nobody notices the first aiptasia. It's a translucent speck the size of a grain of rice, tucked in a crack in the rockwork, and it looks like nothing. Three weeks later there are a dozen of them, and scraping one off with a toothpick just seems to make two more show up in its place.
Quick answer: Aiptasia (Exaiptasia diaphana) is a pest anemone with long, tapering, translucent-to-brown tentacles that spreads mainly by fragmenting itself which is exactly why scraping or tearing it out usually backfires. The three treatments reefers actually reach for are peppermint shrimp (biological), Joe's Juice (a chemical fed directly to the polyp), and kalkwasser paste (a DIY caustic injection) each works, but they suit different situations.
How do you identify aiptasia in a reef tank?
Aiptasia looks like a miniature palm tree: a short polyp body topped with an oral disc ringed by long, thin, tapering tentacles that flare out when the tank is calm and vanish into the rock the instant something disturbs the water. Color ranges from nearly clear to light brown or tan, depending on how much zooxanthellae (the same symbiotic algae that colors coral) the individual polyp is hosting. Most stay under an inch across, though established ones can push toward two inches. The tentacles carry stinging cells (nematocysts) strong enough to make neighboring coral polyps close up and, over time, stress out permanently if a colony gets too close.
The giveaway that separates aiptasia from a coral you actually want is how fast it retracts and how it shows up usually alone at first, in a crack or on the underside of a rock, often riding in on a piece of live rock or a coral frag nobody dipped.
Why one aiptasia turns into a colony so fast
The short answer is fragmentation. Aiptasia reproduces asexually through a process called pedal laceration, where small pieces of tissue break away from the base of the polyp and drift off to settle somewhere new in the tank each fragment capable of growing into a fully independent anemone. That's precisely what makes the instinctive response so counterproductive: scraping, tearing, or squeezing an aiptasia without removing it completely tends to shed tissue into the water column, and a tank that had one aiptasia that morning can have several by the following week.
Aiptasia can also reproduce sexually, though that pathway matters less day-to-day than fragmentation does. And a lot of outbreaks never had a single "patient zero" moment at all they arrived as an unnoticed hitchhiker on new live rock or a coral frag, then multiplied in the weeks before anyone spotted it. They're opportunistic and hardy by nature, which is a big part of why they establish and spread faster than most reefers expect.
The three treatments reefers actually reach for
| Method | How it works | Best for | Watch out for |
|---|---|---|---|
| Peppermint shrimp | Natural predator eats the polyp directly | Small-to-moderate outbreaks, tanks that can host another shrimp | Species confusion only some Lysmata species reliably eat aiptasia; shrimp go off-target if overfed |
| Joe's Juice | A proprietary solution fed straight into the polyp's mouth via syringe | Precise, one-at-a-time removal, including awkward spots in the rockwork | Slow for a large infestation it treats one polyp at a time; flow needs to be off while you work |
| Kalkwasser paste | Concentrated calcium hydroxide burns the polyp on contact when injected | A free DIY option if you already dose kalk | The paste is highly caustic drift onto coral or skin can burn; needs a steady hand |
Peppermint shrimp: biological control, if you get the species right
Peppermint shrimp are the most talked-about "set it and forget it" option, but the category hides a real catch: not every shrimp sold as a peppermint shrimp reliably eats aiptasia. Lysmata boggessi has the strongest reputation as a consistent aiptasia-eater, while the more commonly available Lysmata wurdemanni is frequently sold under the same common name and is less dependable at the job. If your shrimp seem to be ignoring an obvious infestation, the more likely explanation is either the wrong species or a shrimp that's simply too well fed peppermint shrimp will happily eat flake and frozen food instead of aiptasia if there's plenty of it around, so holding back supplemental feeding for a stretch is often what tips them into actually hunting. They're otherwise hardy and low-maintenance, though they're vulnerable to larger predatory fish like lionfish, big wrasses, and dottybacks, and can occasionally pick at LPS coral if aiptasia runs short.
Joe's Juice: precise, but one polyp at a time
Joe's Juice is a chemical treatment applied with a syringe and blunt applicator tip directly into the mouth of the aiptasia polyp no injection into the water column, and the manufacturer markets it as having no measurable effect on water chemistry when used as directed. Flow typically needs to be paused during treatment so the solution stays put long enough to work, and results are usually visible within minutes as the polyp recedes and dies back. The tradeoff is throughput: because each polyp gets individually dosed, Joe's Juice is a strong fit for a handful of stubborn aiptasia in awkward spots, but a slow, tedious one for a tank that's gone from a few to a few dozen.
Kalkwasser paste: free, but it takes a steady hand
Kalkwasser paste is the classic DIY route for reefers who already keep calcium hydroxide powder around for dosing. Mixed with a small amount of RO/DI water into a thick paste and drawn into a syringe with a fine needle, it's injected directly into the base of the polyp, where its high pH essentially chemically burns the tissue from the inside. It costs almost nothing beyond a syringe, but the same causticity that kills the aiptasia can damage coral tissue or skin if the paste drifts or you're heavy-handed with the syringe, and RO/DI water rather than tap water matters for keeping the rest of the tank's chemistry undisturbed.
Which one should you actually reach for?
A single aiptasia or two, tucked somewhere you can get a syringe to, is exactly what Joe's Juice or kalk paste is built for precise, contained, done in one sitting. A tank that's already got a spreading population across multiple rocks is a better fit for a properly identified peppermint shrimp doing ongoing work in the background, rather than hand-treating every polyp one at a time. Either way, the same rule holds: don't scrape, don't tear, and don't disturb an aiptasia you're not prepared to fully remove a wounded polyp left behind is usually how one becomes several.