Coral STN RTN Emergency Protocol Guide: Tissue Loss Triage

Watching tissue peel off an SPS colony is one of the worst hours in reefkeeping, and the speed of your response decides whether you save the genetics. A clean coral STN RTN protocol separates slow tissue necrosis from rapid tissue necrosis, identifies the trigger, and stages the response from quarantine through fragging to recovery. This guide from Gensou Aquascaping at 5 Everton Park captures the triage steps that experienced Singapore reefers use to salvage colonies.

STN vs RTN Distinction

Slow tissue necrosis advances 1-3 mm per day from base or tip and usually ties to chronic chemistry drift — alkalinity swing, low magnesium, or trace metal contamination. Rapid tissue necrosis sloughs tissue in hours, often overnight, and points to acute trauma — a lighting shock, salinity crash, bacterial infection or recent doser overshoot. The treatment paths diverge sharply.

First-Hour Response

Test the full panel: salinity 1.025-1.026, alkalinity 7.5-9.5 dKH, calcium 420-450 ppm, magnesium 1280-1350 ppm, nitrate 1-10 ppm, phosphate 0.03-0.10 ppm, temperature 25-26°C. Note any reading outside range — the trigger usually shows here. Snap reference photos for damage tracking. Stock emergency test kits in the water care range.

Isolation Decision

If RTN is advancing visibly, isolate the colony into a separate quarantine container or frag rescue tank within the hour. Bacterial RTN spreads to neighbouring frags through water-borne pathogens. STN typically does not spread but isolation lets you observe response without reef chemistry confounding the read. A 10-litre isolation cube with heater, low light and a small powerhead suffices.

Fragging the Healthy Tissue

Cut healthy tissue 2-3 cm above the necrosis line using a coral bone cutter or diamond tile saw. Dip the frags in a coral dip — Bayer Advanced Complete Insect Killer at 25 ml per litre for 5 minutes, or Coral RX Pro at label rate — to clear bacteria and pests. Mount frags on plugs or eggcrate using cyanoacrylate gel and place in low-light, low-flow position for the first 14 days.

Iodine Dip for Bacterial RTN

Brightwell Lugol’s Solution or Aquaforest Iodum at 5 drops per litre for 10 minutes is the classic bacterial dip. Rinse the coral in fresh saltwater after dipping. Repeat dipping every other day for the first week if RTN continues advancing. Iodine kills surface bacteria and supports tissue regrowth at low concentrations.

Chemistry Stabilisation

If alkalinity sits outside the 7.5-9.5 dKH window, correct slowly at 0.5 dKH per 24 hours maximum. If magnesium reads below 1280 ppm, dose Tropic Marin Bio-Magnesium to bring it back. Avoid adjusting more than one parameter simultaneously — diagnostic clarity matters more than speed once the colony is fragged. Browse correction products in the aquarium equipment range.

ICP During the Recovery

Send a sample to ATI Coral Lab or Triton within 48 hours of the event. Heavy metal contamination — copper, aluminium, zinc — is the hidden cause behind half the unexplained STN events. ICP results return in 5-7 days and either confirm a contaminated source for replacement, or rule out trace metals so you can focus on chemistry drift instead.

Light Reduction During Recovery

Drop the coral’s light exposure to 30-40 per cent of normal PAR for the first 14 days post-event. High light stresses recovering tissue and accelerates bleaching. Use the AI Hydra or Kessil controller to reduce intensity gradually back to normal across two weeks once tissue regrowth resumes.

When to Stop Fighting

If RTN consumes more than 70 per cent of the colony before isolation, salvage the remaining 30 per cent as multiple small frags, accept the genetic loss of the parent colony and focus on growing out the saves. Persistence on a colony already past the recovery threshold delays regrowth on the daughter frags. Cut your losses early and protect the genetics.

Related Reading

• Coral Brown Jelly Disease Treatment Guide
• Coral Acclimation Light Ramp Guide
• Reef Alkalinity Test Cadence Trending Guide
• Reef ICP vs Hobby Kit Comparison Guide
• Reef Magnesium Imbalance Fix Guide