Coral Aggression Warfare Guide: Sweeper Tentacles and Placement
Corals are sessile but they fight brutally. Acid-tipped tentacles, chemical toxins secreted into the water column, and slow overgrowth competitions all play out across a reef tank, and every losing frag costs you tens or hundreds of dollars. This coral aggression warfare guide from Gensou Aquascaping at 5 Everton Park maps sweeper-tentacle ranges, identifies the worst allelopathic offenders, and lays out a placement framework that keeps peace in a small tank. HDB-sized reefs of 100 to 300 litres force closer quarters than any Western hobby article assumes, so the rules shift here.
Mechanisms of Attack
Three weapons. Physical sweeper tentacles, which extend at night and burn any tissue they touch. Nematocyst-loaded mesenterial filaments ejected from polyps onto neighbours. And chemical allelopathy, soft corals and zoanthids releasing terpenoids and palytoxin analogues into the water column. You can see the first two. The third is invisible and explains tanks where SPS slowly pales without any obvious cause.
Sweeper Tentacle Ranges
Euphyllia species top the aggression chart. Torch, hammer and frogspawn sweepers reach 10 to 15 cm at night, not the daytime polyp size. Galaxea astreata is worse, with 20 cm reach and almost instant tissue melt on contact. Large-polyp stony brain corals extend sweepers around 8 cm.
Buffer accordingly. A torch coral in a nano tank needs a 20 cm clear radius to every non-Euphyllia neighbour.
Chemical Warfare Offenders
Sinularia and Sarcophyton leather corals release terpenoid cocktails that suppress SPS growth across an entire tank. Zoanthid polyps and palythoa produce palytoxin that inhibits coral neighbours. Xenia releases diterpenes that stress acropora within 3 metres.
Counter with aggressive skimming, weekly 15 percent water changes, and activated carbon rotated every two weeks. Singapore tap water post-RODI is clean enough that fresh saltwater rapidly dilutes allelochemicals.
The Placement Hierarchy
Top zone, high light and flow: SPS acropora and montipora, most aggressive to slower-growing neighbours but weakest chemical warriors. Mid-zone: LPS like chalice, acan and brain corals, strong sweepers, plan gaps. Bottom zone: mushrooms, leathers, zoanthids, chemical warriors, physical weaklings.
Do not mix zones vertically if space is tight. Rising allelochemicals from leathers at the base will hit acros at the top regardless of flow direction.
Euphyllia Compatibility Sub-Rules
Torch, hammer and frogspawn corals are all Euphyllia and may fuse safely if the same species, but cross-species contact is 50-50. Glabrescens and paraancora torches specifically often attack their own genus. Keep 15 cm between any two Euphyllia colonies unless you have personally verified the fusion.
Galaxea: The Reef Tank Bully
Beautiful coral, devastating neighbour. Galaxea sweepers reach 20 cm and kill on touch. If you must keep one, isolate on its own island with 25 cm clear radius. Better yet, move it to a frag tank.
Soft Coral Management
Xenia and anthelia propagate like weeds and release diterpenes that stunt SPS growth. If you run a mixed reef, contain them on a removable rock or separate species tank. Never let xenia establish on main rockwork; removal involves scraping and will not succeed fully.
Kenya tree, finger leather and toadstool leathers shed waxy coats every few weeks. Blow off the mucus with a turkey baster before it settles on neighbours.
Physical Barriers and Islands
Rock islands separated by sand channels at least 8 cm wide prevent encrusting overgrowth. Acrylic dividers buried in sand are ugly but effective for known bullies. Frag racks elevate young corals above sweeper range during the six-month acclimation window.
Night Observation Protocol
Once a month, turn off lights for 90 minutes then observe with a red torch. Sweeper tentacles that stay hidden during daytime inspections will be fully extended. Mark suspect colonies and shift neighbours the next day, not during the observation itself.
Recovery from Coral Burns
A burned coral with less than 20 percent tissue loss usually recovers if moved immediately to a low-flow, moderate-light area. Elevated iodine dosing at 0.06 ppm supports tissue regeneration. If tissue is receding after 48 hours, frag the healthy portion onto a fresh plug and discard the damaged base.
Planning Placement Before You Buy
Sketch your scape on paper with final adult sizes noted, not frag sizes. Acros triple in two years. Brain corals inflate to three times their retail footprint. A mixed reef placement plan costs nothing to redraw; a burned $200 torch colony is permanent.
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