The Fluval Flex 2.0 Aquarium Kit, Black is the second-generation Flex at 34 litres, with RGB and white LED lighting, a rebuilt rear filter compartment and a hinged cover.

Key Features

• Measures 35 x 34 x 33 cm and holds 34 litres
• RGB plus white LED at 6500–7000K, with remote control
• Rear multi-stage filtration: an oversized foam block, a Poly-Carb cartridge for mechanical and chemical duty, and ultra-porous BIOMAX for the bacteria
• Dual output nozzles that adjust independently, plus an optional spray bar
• Hinged rear cover, power cord channel, feeding port and cover risers for airflow
• Whisper-quiet pump with a rubberised belt and feet
• Designated heater channel (heater sold separately)
• Made by Fluval, the aquatics brand of Rolf C. Hagen, which has been building aquarium filters since 1975

Setting It Up

• Put it where it will live before you add water. A full aquarium cannot be moved, and glass on an uneven surface cracks
• Check what the furniture underneath can take. Water weighs a kilo a litre before you add glass, gravel and rock
• A new tank has no bacteria in it. Cycling — running the filter for several weeks until it processes ammonia and nitrite to zero — has to happen before fish go in, or they sit in their own waste while the bacteria catch up
• Plant it and let it settle for a few weeks before the first fish. A tank that has been running a month is a far kinder place to arrive in
• Add fish a few at a time, not all at once

Living With It

• Service the foam block in old tank water; change the Poly-Carb cartridge monthly
• Never wash biological media in tap water and never replace it all at once. Chlorine kills the bacteria living on it, and changing everything together restarts the cycle
• Fit the spray bar for a betta or a planted tank
• About 8 hours of light a day is plenty
• Unplug anything electrical before putting your hands in the tank

Good To Know

• Stocking is the thing beginners get wrong. Ask what the fish grows into, not what it is in the shop — most tropicals sold at 2 cm do not stay that size
• Nothing in this kit heats the water unless stated. Tropical fish need a heater; a heater is sized at roughly 1 watt per litre
• A liquid test kit for ammonia, nitrite and nitrate tells you more about a tank than anything you can see
• Most tanks want 20–30% of the water changed weekly, with the replacement dechlorinated and matched for temperature
• 34 L is genuinely small. It is a good betta tank or a shrimp tank, or a home for one small shoal — not a community of several species
• The 34 L has a single media cartridge where the 57 L has the three-basket stack. If you want the configurable filtration, buy the larger one
• No heater included, and a betta or any tropical fish needs one