Keep Your Reef Cosy: The Coral Centre Winter Heater Guide
The clocks have gone back, the central heating is flicking on and off, and somewhere in your living room a tank full of corals is hoping you've thought about this. Good news: winter-proofing a reef isn't complicated. Here's what we tell people at the counter.
What temperature should my reef be?
Most reefs are happy at 25–26°C. Pick a number and stick to it. Stability matters far more than the exact figure. Your corals don't mind 25 or 26. What they hate is 24 at 6am and 27 by teatime. Aim to keep daily swings within about 1°C.
How big a heater do I need?
A good starting point is roughly 1 watt per litre of total water, counting display and sump. Go higher if the tank lives in a cold room, conservatory or garage that really drops overnight.
Better still, split it across two heaters. On a 400L system, run two 200W heaters rather than one 400W. If one dies, the other keeps things ticking over. If one sticks on, it struggles to cook the tank by itself. Put them in the sump where there's good flow.
The bit most people miss: heaters fail ON
A heater that dies is annoying. A heater that sticks on can wipe out a tank overnight.
That's why we always recommend running heaters through a temperature controller. It cuts the power when the water hits your set point, whatever the heater's own thermostat thinks. Options we stock include the D-D Dual Temp Controller TC125, or a Red Sea ReefControl and powerbar which sends alerts to your phone.
Pro tip: set the heaters' own dials about 1°C above the controller. The controller does the day job, and the heater's thermostat is your backup if the controller ever sticks. That gives you two safety nets instead of none.
Don't trust the dial
Heater dials are often a degree or two out. Keep a separate thermometer in the tank and check it against your controller now and then. If they disagree, work out why before changing anything.
Watch your top-off
Central heating dries the air, so tanks evaporate faster in winter. Check your ATO reservoir more often. If you top up by hand, keep an eye on salinity creeping up.
The clocks went back. Did your timers?
Smart lights usually sort themselves out, but plug-in timers won't. Give your lighting and dosing a quick check.
Power cuts
A reef holds its heat better than you'd think. A few hours without power is rarely the disaster it feels like. What matters most is keeping the water moving and oxygenated.
- Keep a battery air pump in the cupboard. It's cheap, and you'll thank us.
- Wrap the tank in blankets or a duvet to hold the heat in.
- Don't feed until the power's back.
- When it returns, check that everything has restarted: return pump, heaters, controller and timers.
Water change safety
Unplug heaters before the water level drops, and give them 15 minutes to cool before they come out. A hot glass heater meeting air or cold water can crack. While you're there, check every cable has a drip loop and everything is on an RCD.
Away for Christmas?
Ask someone to check in daily. Leave them a short note with your target temperature, what "wrong" looks like, and our number. Ask them to ring us rather than fiddle.
Not sure about your setup?
Pop into Coral HQ or give us a shout, and we'll tell you whether your heating's up to the job. If you'd rather we did the worrying, our maintenance team can give your system a full winter check.
Stay warm. Your corals certainly intend to.