Emergency Response Manual for Coral Tanks | Bleaching, RTN, Power Outages

Maintaining a coral tank inevitably means encountering emergencies at some point. Bleaching and RTN (Rapid Tissue Necrosis) can result in the loss of precious corals in just hours, and ignoring power outages or heater failures can cause catastrophic damage. This article explains how to identify the signs of each emergency and the specific steps to minimize damage.

RTN (Rapid Tissue Necrosis): Occurrence and Initial Response

RTN is a terrifying condition where coral tissue rapidly peels away and becomes necrotic in hours to overnight. It primarily affects SPS (hard corals) such as Acropora and branching corals, characterized by exposed white skeleton. For those wanting to master the tips for long-term maintenance, Coral Tank Long-Term Maintenance Guide is also helpful.

• Early Detection: Watch for when polyps fully retract and the tissue edge begins to recede with a white appearance. A clear boundary line between healthy and affected tissue is typically visible
• Immediate Isolation: Remove any coral showing RTN from the main tank immediately. RTN is contagious and can spread to the same species or related species
• Fragging: If necrosis is still progressing, separate healthy tissue sections using a frag saw or bone cutter. Cut at least 2 cm away from the necrotic area
• Iodine Dip: Dip the separated frag in diluted Betadine (povidone-iodine) or Coral Rx for 5–10 minutes
• Investigate the Cause: Common triggers include sudden alkalinity swings (more than 1 dKH per day), rapid temperature increases, and heavy metal contamination

STN (Slow Tissue Necrosis): Management

STN progresses more slowly than RTN, but delayed response is equally fatal. Tissue recession occurs over days to weeks.

• Characteristics: Tissue gradually recedes upward from the base. Because it's not as rapid as RTN, daily observation can enable early detection
• Check Water Parameters: Verify calcium (400–450 ppm), alkalinity (7–9 dKH), and magnesium (1250–1400 ppm) levels, and check for sudden fluctuations
• Review Lighting and PAR: If STN begins shortly after changing lighting, light stress may be the cause. Measure PAR with a meter and verify the coral is within its proper range
• Adjust Water Flow: Inadequate flow at the coral's base leads to detritus accumulation, causing tissue necrosis
• Fragging Decision: If progression doesn't stop, attempt to save healthy sections with fragging as with RTN

Bleaching: Initial Response and Cause Identification

Bleaching is the loss of zooxanthellae and doesn't necessarily mean death. Early response can lead to recovery. Temperature management to prevent heat-stress bleaching is covered in detail in Coral Heat Stress Management.

• Light-Stress Bleaching: Common after lighting upgrades or repositioning in the tank. Reduce light intensity by 20–30% and gradually restore it over 1–2 weeks
• Temperature-Stress Bleaching: Bleaching risk spikes when water temperature exceeds 28°C. Cool with a chiller or fan to below 26°C. Avoid rapid cooling; reduce temperature at a rate of 1°C per day
• Chemical-Stress Bleaching: Trace amounts of heavy metals like copper or zinc, or pesticides, can trigger it. Attempt removal through a large water change (50%) and activated carbon
• Nutrient-Deficiency Bleaching: In ultra-low nutrient conditions, corals may starve. If nitrate is below 0.5 ppm, supplement with amino acid additives or coral food
• Recovery Timeline: Zooxanthellae typically return 2–8 weeks after the cause is removed. Constantly adjusting conditions is counterproductive

Emergency Response During Power Outages

Power outages are a serious threat to coral tanks. Oxygen supply, temperature maintenance, and water circulation all stop simultaneously.

• Oxygen Supply is Top Priority: Keep a battery-powered air pump on hand to prevent hypoxia in corals and fish. Available for around ¥1,000, it can be lifesaving. Prioritize this especially if keeping oxygen-sensitive invertebrates like giant clams
• Temperature Maintenance: In winter, temperature drop during an outage is fatal. Insulate the tank with blankets or foam, and apply disposable hand warmers to the outside to extend survival by hours. In summer, remove the cover to allow natural heat dissipation
• Surface Agitation: An air pump doubles as surface agitation. Without one, gently stir the water by hand every 30 minutes to promote oxygen exchange
• Prevent Protein Skimmer Backflow: During a power outage, dirty water can flow backward from the skimmer into the tank. Install a check valve beforehand, or clamp the skimmer's drain line as soon as the power goes out
• UPS (Uninterruptible Power Supply): Connecting critical equipment (circulation pump, heater controller) to a UPS provides peace of mind. A 600 VA UPS can run a circulation pump for several hours

Preparing for Heater Failure

Heater failures come in two forms: overheating (boiling) and failure to heat (freezing)—both are fatal.

• Prevent Overheating: Always connect a separate temperature controller (thermostat) to the heater. Relying on the built-in thermostat alone is risky. A controller acts as a safety device, cutting power if temperature rises 2°C above the setpoint
• Safeguard Against Heating Loss: Use multiple heaters so if one fails, others maintain temperature. For example, use two 150 W heaters in a tank needing 300 W
• Anomaly Detection: Choose a temperature monitor with alert function and set it to notify your smartphone if temperature falls outside the target range
• Heater Lifespan Management: Standard heaters should be replaced every 1–2 years. Replace with new units before the season begins
• Emergency Heating Method: If water temperature drops due to heater failure, fill a plastic bottle with hot water (about 5°C above tank temperature) and float it in the tank for emergency warming

Checklist of Emergency Supplies

Preparing these items in advance enables quick response when emergencies occur.

• Battery-Powered Air Pump: Essential for power outage preparedness. Regularly check battery expiration
• Coral Rx or Iodine-Based Dip: For fragging during RTN/STN events
• Frag Plugs and Frag Adhesive: Needed for emergency fragging
• Activated Carbon: For absorbing chemical contaminants
• Backup Heater: For immediate replacement in case of heater failure
• Disposable Hand Warmers and Blankets: For insulation during winter power outages
• Water Test Kit: Essential for identifying causes in emergencies (ammonia and nitrite are especially critical)

Find Trustworthy Corals on BreederDirect

On BreederDirect, you can buy corals directly from breeders who openly share their husbandry conditions and management practices. Before purchasing, ask breeders about their emergency response experience—advice from experienced breeders is often more practical than manuals. Welcome healthy specimens, maintain full emergency preparedness, and keep your beautiful coral tank thriving.