🌡️ Heater Stuck ON — Complete Action Plan

🚨 0–30 MIN: Stop the heat & stabilize

• 🧪 Verify the temperature with a separate thermometer (don’t trust the heater dial).
• 🔌 Unplug the heater (do not just turn its dial down).
• 💨 Maximize oxygen immediately (warm water holds less O₂):
  • Turn on extra air stones / sponge filters.
  • Point returns to break the surface (ripples across the whole top).
• 🧊 Begin controlled cooling (1–2 °C / 2–3.5 °F per hour max):
  • Float sealed bottles/bags of ice (never dump ice directly).
  • Put a fan across the water surface (strong evaporative cooling).
  • Open the lid for gas exchange & passive cooling.
• 💡 Dim or switch off lights to cut heat load & fish activity.
• 🍽️ Stop feeding (lower metabolism & ammonia production).

🧭 Emergency thresholds (tropical tanks)

• 30 °C / 86 °F → start active cooling
• 32 °C / 90 °F → critical cooling (add partial water change with slightly cooler water)
• 35 °C / 95 °F → life-threatening; combine all methods and prepare a temporary bin

---

⏳ 30–120 MIN: Controlled temperature drop

• 🧊 Keep cooling gradual: target 1–2 °C per hour (fast drops shock fish).
• 💧 Partial water change (20–30%) with dechlorinated water ~2–3 °C (3–5 °F) cooler only if temp > 32 °C / 90 °F. Match pH/KH/GH as closely as possible.
• 🔁 Cycle ice bottles: when melted, swap for fresh frozen ones.
• 🫧 Maintain strong aeration the whole time (warm water = low O₂ + higher fish O₂ demand).

---

🐟 2–24 H: Observation & recovery

• 👀 Watch respiration: rapid gills, surface “piping” = add even more agitation.
• 😵 Heat stress signs: lethargy, loss of equilibrium, darting, color wash-out.
• 🧪 Test ammonia/nitrite (0/0 target). Heat spikes can suppress biofilter.
• 🧊 Keep a few ice bottles rotating if room is hot; aim to stabilize at your normal setpoint.

---

❄️ How much cooling power do you need?

🧮 Estimating ICE required (sealed in bags/bottles)

Use this rule-of-thumb (freezer ~−18 °C / 0 °F):

• Why this works: Each kg of freezer ice absorbs ≈370 kJ warming to 0 °C and melting; each kg of evaporated water removes ≈2260 kJ.
• ✅ Best practice: combine fans + ice for strong, controlled cooling (and top off evaporated water with dechlorinated/RO).

---

🔥 How fast can a stuck heater overheat a tank?

Approximate heating rates if a heater is fully ON:

A 300 W heater can push a 200 L tank >1.2 °C per hour if it sticks ON — that’s why quick action matters.

---

🧰 Triage options (if temperature keeps rising)

• 🪣 Emergency tote/bin (food-safe): move the most sensitive fish first. Use airstone, same tank water, and ice outside the container (sealed) to control temp.
• 🪵 Shade & hiding: reduce visual stress; keep room lights low.
• 🧴 Ammonia binder (e.g., conditioner) if filters were disrupted; still maintain strong aeration.

---

🧪 What to do with the heater afterward

• ❌ Do not reuse the heater until tested (preferably replace it).
• 🧪 Bucket test with an external thermometer:
  • Put heater in a bucket, set to a modest temp (e.g., 26 °C / 79 °F).
  • Observe whether it clicks off and holds within ±0.5–1.0 °C for 1–2 hours.
  • Any failure to switch off = trash it.
• 🔍 Inspect for moisture under the cap, cracked glass, scorch marks — toss if any are present.

---

🛡️ Long-term prevention (highly recommended)

• 🧠 External temperature controller (independent thermostat cuts power if tank overheats).
  • Set controller to your normal temp (e.g., 26.0 °C), and heater dial 0.5–1 °C higher (controller is the boss).
• ♻️ Two smaller heaters instead of one big one (e.g., 2×150 W vs 300 W). If one sticks ON, it heats slower.
• 🧯 Ambient safeguards: keep tanks out of direct sun; ensure room ventilation.
• 🔁 Replace heaters proactively every 2–3 years; they’re consumables.
• 🧪 Two thermometers (digital + floating) so one can catch failure of the other.
• 🔔 Temp alarm (standalone or controller alarm) to alert at ≥30 °C.
• 🧊 Keep a freezer kit: 6–12 × 1 L bottles pre-filled and frozen, labeled “FISH TANK — DO NOT DRINK”.
• 💨 Spare air pumps (battery/USB) — warm water = low O₂; air saves lives during heat events.
• 🧪 Log daily temp in a notebook/app; trends reveal creeping issues early.

---

🧬 Species sensitivity cues (who to watch first)

• 😰 High-risk: stingrays, discus, wild plecos, certain catfish — watch for rapid gilling and listlessness at ≥30 °C.
• ⚠️ Moderate: most community tropicals — stressed by ≥31–32 °C if sudden.
• 🙂 More tolerant (short term): some livebearers and labyrinth fish — still add air; don’t rely on tolerance.

---

🧾 Quick emergency checklist (print and tape near the tank)

• 🛑 Unplug heater
• 🧪 Confirm temp on separate thermometer
• 💨 Max aeration + surface ripples
• 🧊 Ice bottles + fan (target 1–2 °C/hr drop)
• 💡 Lights off / room dim
• 💧 20–30% water change with slightly cooler dechlorinated water if >32 °C
• 👀 Watch breathing & behavior; continue gradual cooling
• 🗑️ Retire or replace faulty heater; add controller before next use.