RTN (Rapid Tissue Necrosis) is exactly what it sounds like - a coral colony loses tissue from the base or a single branch outward at a visible rate, sometimes within hours. STN (Slow Tissue Necrosis) is the same disease process running at a slower clock, often spreading over days to weeks. The exposed white skeleton is what you see; the dead coral is just the most obvious symptom. Both are typically triggered by an environmental stress event followed by bacterial infection that takes hold in the stressed tissue.
When you spot RTN/STN, action comes before investigation. Get the affected colony into a separate container with tank water and an air stone. Use a Dremel or coral saw to remove every section of skeleton with active tissue loss, cutting at least 1 cm into healthy tissue. The healthy fragments go into a frag tank or a separate quarantine container with strong flow. The diseased material is discarded. Skip dipping the original colony - dipping after a major loss adds stress to already-failing tissue.
Once the colony is fragged and stable, audit every parameter you can test. The majority of RTN events trace to one of: alkalinity swing greater than 1 dKH in 24 hours, salinity drift outside 1.024-1.027, temperature spike or crash, low oxygen at night, or an over-dose of a supplement. Pull a complete ICP test from Triton or ATI - many cases trace to a heavy-metal contamination (copper, aluminum, iron) that no hobbyist test kit detects. The colony was not failing for no reason.
Healthy fragments from an RTN colony go into low to moderate flow with moderate light for at least 2-3 weeks. Drop them in a frag rack 12-15 inches below your light source and resist the urge to move them. Encrustation on the cut sites is the first sign of survival - you should see polyp extension and color return within a week if the frag is going to live. Dose amino acids 2-3 times per week to support regrowth.
Stable alkalinity is the single biggest preventative measure for SPS-dominant tanks. Once you have more than three or four colonies, manual dosing is not enough - install a calcium reactor, a two-part doser, or a kalk reactor with consistent output. Quarantine and dip every new SPS specimen with CoralRx or Bayer Advanced Insect Killer (yes, that one - reef hobbyists have used it for years). Run a UV sterilizer if you have unexplained losses, since some bacterial agents implicated in RTN are killed by UV exposure.
Recommendations on this page cross-checked against the following authoritative references and our internal vendor + breeder database.
Answers to the questions experienced keepers ask after the basic care guide.
Drip acclimation over 60 to 90 minutes is the safest approach for RTN and STN: triage protocol for tissue necrosis on SPS coral - Fast Aquatics. Match temperature first (15 minute float), then drip 2 to 3 drops per second from the display sump until the bag volume has tripled. Test salinity (or freshwater hardness) at the end - if it is within 0.001 SG (or 2 dGH) of the display, transfer the specimen with a net rather than pouring shipping water in.
Aim for biological + mechanical + chemical staging. Canister or sump-driven filtration sized for 5x to 8x display turnover per hour, mechanical floss replaced weekly, and carbon or GAC swapped every 4 to 6 weeks. RTN and STN: triage protocol for tissue necrosis on SPS coral - Fast Aquatics responds well to stable nitrate (under 20 ppm) more than to any specific filter brand - stability beats peak performance.
For saltwater specimens, yes - a properly-sized skimmer rated for 1.5x to 2x display volume keeps dissolved organics low and reduces nuisance-algae triggers. Freshwater specimens do not need skimmers; a well-stocked plant grow-out + canister with chemical media achieves the same end. RTN and STN: triage protocol for tissue necrosis on SPS coral - Fast Aquatics kept without adequate organic export tends to show stress within 90 days.
Compatibility with planted tanks depends on the species behavior + water chemistry overlap. Plant-safe specimens leave foliage alone; some pick at soft-tissue plants like vallisneria or anubias. Check the species page profile + the planted-tank compatibility note before stocking RTN and STN: triage protocol for tissue necrosis on SPS coral - Fast Aquatics in a high-tech CO2-injected setup with valuable cultivars.
For freshwater specimens with no plant requirements, a basic LED at 30 to 50 PAR at substrate is sufficient and reduces algae. For saltwater + reef specimens, target 100 to 250 PAR depending on photo-tolerance, with a sunrise/sunset ramp + a 8 to 10 hour photoperiod. RTN and STN: triage protocol for tissue necrosis on SPS coral - Fast Aquatics tolerates a wider lighting band than most keepers expect; consistency matters more than peak intensity.
Most aquarium species evolved in moderate flow with localized turbulence rather than uniform high flow. Aim for 20x to 40x display turnover for reef specimens, 4x to 6x for community freshwater. RTN and STN: triage protocol for tissue necrosis on SPS coral - Fast Aquatics shows stress fins (clamped, frayed) when flow is mismatched - dial back if you see this within 14 days of introduction.
Sustained drift above +/- 2 F from target is the threshold most keepers miss. RTN and STN: triage protocol for tissue necrosis on SPS coral - Fast Aquatics tolerates day-night swings of 1 to 2 F without issue but a 4 F shift over 2 hours triggers ich + bacterial bloom risk. Use a controller-driven heater (not the built-in dial) and a backup thermometer at the opposite end of the tank.
For freshwater fish: ich, columnaris, and fin rot are the top three; quarantine + UV sterilizer prevents the majority. For marine fish: ich (Cryptocaryon), velvet (Amyloodinium), and bacterial infections; tank-transfer method or copper QT during the 30-day acclimation cycle prevents nearly all outbreaks. For inverts + corals: tissue necrosis, parasitic isopods, and protozoan blooms.
Captive breeding success varies enormously by species - some breed readily in community tanks (livebearers, cherry shrimp, clownfish) while others have never been captive-bred (most reef fish + most marine inverts). Check the species-specific care guide for the breeding-method note + larval-rearing protocol. RTN and STN: triage protocol for tissue necrosis on SPS coral - Fast Aquatics kept in pairs or small groups often spawns even without intent if conditions are right.
Avoid same-species rivals (especially male-male pairings for territorial species), known fin-nippers (tiger barbs, certain pufferfish), and anything that out-competes for food or out-grows the tank. RTN and STN: triage protocol for tissue necrosis on SPS coral - Fast Aquatics also struggles with hyper-aggressive cichlids in freshwater and damselfish in saltwater - both will hold territory at the expense of every other tankmate.
Most ornamental specimens accept cleaner shrimp + cleaner gobies; cleaner wrasses (Labroides) often die in captivity and are not recommended. RTN and STN: triage protocol for tissue necrosis on SPS coral - Fast Aquatics kept with cleaner pairs typically benefits from parasite control + stress reduction, but verify the cleaner does not get eaten by checking the species size + temperament chart.
Captive lifespan tracks closely to wild lifespan when water chemistry, diet, and tankmate stress are managed. Most aquarium fish live 5 to 12 years; long-lived species (large cichlids, pufferfish, some tangs) reach 15+ years. RTN and STN: triage protocol for tissue necrosis on SPS coral - Fast Aquatics kept in a stable, properly-sized system should live within 80% to 100% of the species lifespan ceiling - early death usually traces back to chronic-stress causes (parameters, tankmates, diet) rather than disease.