Submersible glass heater
Standard. Glass tube fully submerged, dial thermostat. Eheim Jager (gold standard, 25–300 W), Fluval E series (digital). Replace every 3–5 years — thermostats stick with age. Glass = breakable, careful when removing.
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Heaters And Thermometers
🌡️ Heaters + thermometers
Aquarium heaters & thermometers — get sizing + safety right
A stuck heater can boil a tank in 6 hours. A failed heater drops temperature 5–10 °C overnight in an Irish winter. Tropical fish die in either direction. Two cheap fixes — correct wattage + a backup thermometer — save your stock. Here's the kit + the rules.
What we'll be stocking
Heater + thermometer types
Submersible plastic / titanium
Tougher than glass. Titanium for big tanks (200 L+), plastic for cheap small tanks. Slightly more expensive. Less common but unbreakable. Aquael Ultra Heater is a popular plastic option.
In-line heater (canister-paired)
Installed in the canister filter return hose. Heats water as it returns to tank. Hidden, no in-tank glass tube, more even heating. Hydor ETH series. Adds €40–€80 over standard but invaluable for aquascaped show tanks.
Inkbird / external thermostat controller
Plugs heater INTO the controller. Controller has its own probe in the tank. If heater sticks ON, controller cuts power at set temp. Single best safety upgrade — €30 saves your fish if a heater fails. Inkbird ITC-308 standard.
Stick-on / digital thermometer
Stick-on LCD strips: cheap, less accurate, often wrong by 2–3 °C. Digital probe thermometers: accurate to 0.1 °C, alarms for high/low. Always have ONE thermometer separate from the heater's built-in display — you NEED an independent reading.
Sizing + safety + setup
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Wattage rule — 1 W per litre
Up to 100 L: 1 W per litre (100 W for 100 L). 100–200 L: 1.5 W per litre. 200 L+: 2 W per litre, OR split across TWO smaller heaters (redundancy). Cold rooms in Irish winter: bump up by 25%. Underpowered heater = always-on, burns out + can't hold temp.
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Two heaters, half wattage each
For tanks over 100 L, use TWO heaters at half the rated wattage instead of one big one. If one fails ON: half the wattage = won't boil. If one fails OFF: half the heating still active = no shock-cool. Best safety upgrade in fishkeeping.
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Independent thermometer — non-negotiable
Heater dial is approximate; many run 2–4 °C off the set point. ALWAYS have a separate thermometer (digital or even cheap stick-on) for actual reading. Daily glance during morning routine catches issues fast.
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External controller for show tanks
Inkbird ITC-308 plug-in: heater plugs into the controller, controller has temperature probe in tank. Set 25 °C, controller cuts power at 25.2 °C, restores at 24.8 °C. €30 + €30 heater outperforms a €100 "premium" heater on safety + accuracy.
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Never run a heater dry
Submersible heaters MUST be fully under water during operation. During water changes: turn heater OFF first, wait 15 min before unplugging (thermal shock cracks glass). Heater run dry = boils + glass shatters when refilled. Reset it on the wall + replace soon after — likely thermostat damage.
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Species-correct temperature
Tropical (most community fish): 24–26 °C. Discus: 28–30 °C. Goldfish + minnows + axolotls: COLDWATER 18–22 °C — heater NOT needed in heated Irish home. Bettas: 26–28 °C. Always research species temps before stocking — wrong temp = chronic stress + disease.
📦 We're stocking up
Our heaters and thermometers range goes live as we vet suppliers — we won't list anything we wouldn't use ourselves. In the meantime, our calculators, breed guides and AI vet tools below are free and don't need stock.
Frequently asked questions
How big a heater do I need?
Roughly 1 W per litre for tanks up to 100 L; 1.5 W/L from 100–200 L; 2 W/L over 200 L. Add 25% for very cold rooms in Irish winter. For redundancy + safety, split wattage across TWO heaters in tanks over 100 L.
Why is my heater always on?
Three usual causes: (1) underpowered for the tank size — check wattage, (2) cold-room placement (basement, near outside wall) — insulate or move tank, (3) thermostat failed open (always-on stuck) — replace immediately, this can boil the tank. Always-on with rising temp = same-day replacement.
Do goldfish need a heater?
No — goldfish + fancy goldfish are coldwater (18–22 °C), comfortable in any heated Irish home without supplementary heat. Only exception: outdoor pond goldfish brought in for winter to a cold conservatory. Heating goldfish water shortens lifespan + accelerates ammonia waste production.
My heater controller (Inkbird) seems excessive — is it?
Not at all. A €30 Inkbird ITC-308 with a €25 basic heater outperforms a €120 "premium" heater on safety + accuracy. The controller has its own probe + cuts power if heater fails ON. Single best safety upgrade for any tank with valuable fish.