The short answer
The aim is to preserve attached substrate and avoid cutting through polyps. Keeping a sliver of tile, rock, or plug attached to the mat makes mounting easier and avoids peeling the polyps from their base. It does not guarantee survival. Everything below is built around that one idea.
Safety first: palytoxin
Some zoanthids, especially Palythoa, can contain palytoxin. Color or trade name cannot reliably tell you whether a colony is toxic. Exposure through skin, eyes, or inhaled droplets can cause serious illness. Cutting or breaking coral and rock can create contaminated splashes or aerosols.
This outline is for experienced reef keepers, not a complete safety protocol. Get hands-on guidance before attempting it. Minimize handling, keep coral submerged wherever possible, and work in a well-ventilated area away from food, other people, and pets. Wear robust, long protective gloves, splash goggles, and protective clothing. Appropriate, properly fitted respiratory protection is also advised; NCCEH recommends P100-level protection. PPE and ventilation do not eliminate the risk.
Never boil, heat, steam, microwave, pressure-wash, brush, or scrub coral-covered rock or plugs. Do not use a powered saw for the method described here. Avoid splashing, spraying, and touching your face; wash your hands after handling.
If you suspect exposure, stop and seek urgent medical advice, mentioning possible palytoxin exposure from aquarium coral. For breathing difficulty, call emergency services immediately. Leave the affected area if aerosols are suspected and get professional advice before cleanup.
Safety guidance: CDC exposure investigation, NCCEH evidence brief, and OATA handling guidance.
What you need
- A fresh scalpel or razor blade
- Manual coral cutters suitable for the thin tile or plug you are using
- Thick super glue gel (cyanoacrylate gel)
- Empty 1 inch frag plugs, soaked in tank water ahead of time
- Paper towels and tweezers
- Clean, dedicated containers of tank water for holding and rinsing, plus a separate dip container if needed
- An appropriate coral dip, only if needed and used according to its current label
- The protective equipment described in the palytoxin warning above
Before you cut
Only frag a healthy colony that is fully open, growing, and has been settled in your tank. A colony that is closed, shrinking, or newly arrived will punish you for cutting it.
The easiest frags of all are planned months ahead. Grow your mother colony on a 3 inch tile or disc and let it overgrow the edges. When the tile is covered, you are still cutting living connecting tissue, not only tile. Cut between the polyps and minimize damage to the mat; each piece remains attached to its substrate. Colonies growing on open rock are where the harder methods below come in.
The cut, step by step
- Inspect the colony. Keep it submerged and allow the polyps to retract naturally. If you need to move it, transfer it in a water-filled container. Do not lift or repeatedly disturb it just to close the polyps.
- Score the mat. With the scalpel, score through the mat between the polyps, following the natural grooves. Cut as little living tissue as you can.
- Cut the substrate under the line. Use manual cutters suitable for the tile or plug while keeping the coral submerged and avoiding splashes. Never cut through a polyp head. Stop if the substrate requires forceful breaking or powered tools. Submerged handling does not eliminate exposure risk.
- Aim for a manageable group. Three to five polyps is a practical starting point, not a survival rule. Results depend on the colony and conditions; avoid tiny frags while learning.
Working on rock you cannot remove? Slide the scalpel under the mat and take a sliver of rock with it. Peeling bare mat with no substrate works in a pinch, but those frags are the hardest to glue and the most likely to float off, so treat them as the last resort.
Gluing
Slime can interfere with the bond. Prepare only the non-living contact surfaces, keeping handling brief:
- Blot the plug dry.
- Blot only the exposed underside of the rock or tile chip. Do not blot or dry the living mat or polyps.
- Put a pea sized dab of glue gel on the plug.
- Press the chip in gently, follow the glue maker's directions, and return it to the water promptly.
Use as little glue as you can get away with, and keep it off the skirt of the polyps. Use a cyanoacrylate gel labeled for reef-aquarium coral mounting, and follow its directions.
Loose polyp that will not stay glued? Avoid repeated handling, squeezing, or banding the tissue. Ask an experienced coral keeper about a protected, low-flow rubble container; attachment time varies.
The dip
Rinse gently in a separate container of tank water while keeping the frag submerged; avoid spraying or blasting it with a baster. A dip is not a guarantee of healing or a substitute for quarantine. If using one, choose a coral-compatible product for the specific purpose, follow that product's current dose and duration, watch for adverse reactions, and rinse as directed with clean saltwater. Iodine products and pest dips are not interchangeable, and no single recipe fits every product or coral. Never add used dip water to the aquarium. See Seachem Reef Dip directions and Coral Rx guidance.
Healing
Put fresh frags back at about the same light level the mother colony gets, in gentle indirect flow. Not the top of a bright rack, and not a dead corner where film settles on the cut mat. Then leave them alone. Moving a healing frag every day is a quiet killer.
What to expect: reopening and recovery times vary. Opening is not the same as healing, and two weeks is not a deadline or guarantee. Before moving a frag on, look for consistent opening, a secure attachment, and healthy tissue with no continuing recession. Persistent closure or tissue loss calls for investigation, not repeated cutting or dipping.
Mistakes that kill frags
- Cutting through polyps instead of between them
- Fragging a colony that is stressed, closed, or brand new
- Gluing onto a wet, slimy surface and blaming the glue
- Thick glue over living tissue
- Fresh frags in direct, blasting flow
- Making tiny frags before you know how that colony responds
- Handling and moving frags while they are trying to heal
The bottom line
Plan ahead with removable tiles, preserve the attached substrate, minimize tissue damage and handling, and allow recovery in stable conditions. Follow palytoxin precautions and any product directions. These steps can reduce avoidable problems, but fragging always carries risks for both the keeper and the coral.