Fluval P25 Submersible Nano Aquarium Heater - 25W

The Fluval P25 Submersible Nano Aquarium Heater is a 25 watt nano heater in shatterproof polymer, pre-set to hold 24–26°C with no dial to adjust, for small tanks up to roughly 25 litres.

Key Features

• Pre-set to 24–26°C (76–78°F), which is the right range for most tropical community fish and for a betta. There is no dial, which removes the commonest way people get it wrong
• Made from shatterproof polymer rather than glass — the practical advantage in a small tank where a heater gets knocked
• Fully submersible, so it can be laid horizontally along the back or low down where the flow passes it
• 25 watts, sized for nano tanks up to about 25 litres
• For use in both freshwater and saltwater aquariums
• Made by Fluval, the aquatics brand of Rolf C. Hagen, which has been building aquarium filters since 1975

Using It

• Fit it low in the tank, horizontally, where the filter flow runs over it
• Give it 20–30 minutes submerged before switching on
• Because it is pre-set, the only check you need is a thermometer telling you the water is where it should be
• In a UAE summer the room may already be warmer than the set point, in which case the heater simply will not come on. That is normal

Using It Safely

• Unplug anything electrical before putting your hands in the tank
• Switch a heater off and let it cool for fifteen minutes before lifting it out of the water. Hot glass in cold air can crack
• Fit a drip loop — let the cable hang below the socket so water runs off rather than down into it
• Put the heater where the filter flow passes over it. A heater in a dead corner heats that corner and nothing else
• Check the tank temperature with a separate thermometer. A heater's dial is a setting, not a measurement
• Heaters fail. They fail off, which is survivable, and they fail on, which is not. A thermometer you actually look at is the cheapest insurance in the hobby

Good To Know

• 25 W is a nano heater. In a tank much over 25 L it will run constantly and still not hold temperature
• A pre-set heater cannot be turned up for a fish that wants warmer water, or down for one that wants cooler. Check your species' range first
• A betta needs a heater. Unheated room-temperature water is the commonest reason shop bettas do badly at home
• Shatterproof is not indestructible — it is a polymer body, and it still needs the same care as glass