Aquarium heaters
Most tropical fish need water kept within a fairly narrow temperature range, and a stable submersible heater is what does that job around the clock. It's not an optional extra for a tropical set-up — without one, tank temperature simply follows the room, which most tropical species can't tolerate for long.
What we stock
We carry Marina submersible pre-set heaters in 50w and 300w options, sized for different tank volumes rather than one-size-fits-all. Pre-set heaters are calibrated to hold a standard tropical temperature, which takes the guesswork out of dialling in a setting yourself.
Wattage needs to be matched to your tank's actual volume — too low a wattage struggles to maintain temperature in a larger tank, especially in a cold room, while too high a wattage in a small tank risks overshooting and heating the water faster than intended.
Setting one up safely
Always fully submerge a heater before switching it on, and let it adjust to water temperature for around fifteen to twenty minutes after moving tanks or topping up cold water, since switching a cold heater on too quickly can cause it to crack. Position it near a filter outlet where possible, so warmed water circulates rather than pooling in one spot.
A separate aquarium thermometer is worth having alongside any heater, since it's the only real way to confirm the water is actually at the temperature you expect rather than trusting the heater's dial alone.
In this section
Everything below is in stock with us, priced with delivery worked out, and packed and posted by hand in the UK.
Tetra Goldfish Flakes
Complete goldfish flakes in several pack sizes, with a shared formula across the family
From£3.02
Tetra Goldfish Granules
Complete granules for goldfish, with a shared formula across both pack options
From£3.98
Tetra Prima Mini Granules
Slow-sinking granules for mid-water and bottom-feeding fish, blending herbivore and omnivore diets
£6.10
Tetra Aquasafe
A water conditioner that neutralises chlorine and heavy metals, with an added vitamin B mix
From£6.41
Tetra Pond Fish Food Variety Sticks
Complete Tetra Pond Variety Sticks in three colours, across four pack sizes
From£6.41
Tetra Koi Pond Fish Food Sticks
Complete fast-soaking Tetra Pond Koi Sticks, available in four pack sizes
From£6.41
Tetramin
Complete TetraMin flake food for ornamental fish, offered across several pack sizes
From£2.39
Tetra Temperate Flakes
Complete flakes for subtropical fish kept at 18–23°C, with vegetable ingredients
£6.99
Tetra Pond Fish Food Sticks
Complete fast-soaking Tetra Pond Sticks for pond fish, in seven pack sizes
From£4.77
Tetra Japan
Sinking dry pellets for fancy goldfish, with pack-specific label information shown clearly
From£4.56
Common questions
- What wattage heater do I need for my tank?
- As a rough guide, larger tanks need more wattage to maintain a stable temperature, and a colder room means you'll need more wattage than the same size tank somewhere warmer. Check the manufacturer's guidance for your specific tank volume rather than guessing.
- Do I still need a thermometer if my heater is pre-set?
- Yes — a pre-set heater is calibrated at the factory, but a separate thermometer is the only way to confirm your tank is actually holding that temperature in practice, since room conditions and tank size both affect the real result.
- Is it safe to touch a heater once it's been running?
- No, let it cool fully before handling, and never switch a heater on outside of water even briefly, since running it dry can cause it to overheat and break. Unplug it before doing any tank maintenance that involves removing it from the water.
- What happens if my heater fails in cold weather?
- Tank temperature will start to drift towards room temperature, which most tropical fish can't tolerate for long. Keeping a spare heater on hand, or at least checking your thermometer regularly, means a failure is caught quickly rather than discovered days later.
Related
Written by Matt Garnett, who runs Giddy Pets and is a lifelong pet owner — not a vet. This is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your animal. How we write these guides.