Fluval

Fluval is the aquatics brand of Rolf C. Hagen and has been building aquarium filters since 1975. The range here runs from nano tanks to canister filters for 1,500 litre systems, plus the media, pumps, heaters, lighting and spare parts that keep them going. Marina, Hagen's entry-level aquatics brand, sits alongside it.

Filters — which type?

• Hang-on power filters (AC20, AC30, AC70) clip on the back rim. Easy to service, nothing inside the tank, and the right answer for most tanks up to about 250 litres. The newer AC series separates each media stage so you can change carbon without disturbing the bacteria.
• Clip-on with a trickle stage (C-Series, C2 and C4). The trickle chamber runs water over media in the air, where bacteria get far more oxygen — biological capacity closer to a small canister.
• External canisters (07 Series 107–407) live in the cabinet. Only two hoses show in the water, and they hold several times the media of a hang-on filter.
• High-performance canisters (FX2, FX4, FX6) for 750 to 1,500 litres, with Smart Pump control and automatic air purging.
• Powerheads are pumps, not filters. They create current and drive undergravel plates — useful alongside a filter, never instead of one.

Aquariums

• Spec 19 L — a well-made nano with a 7000K aluminium LED. A betta tank, a shrimp tank or a small shoal.
• Flex — curved front glass with the filtration hidden behind the tank, in 34 L, 57 L and 123 L. The Flex 2.0 adds a media stack that lifts out in one piece.
• Sea Flex 123 L — the marine version, with a blue-weighted LED built for corals.
• No aquarium kit in this range includes a heater. Tropical fish need one, sized at roughly 1 watt per litre.

Media, and the one rule that matters

• Mechanical foam traps debris. Activated carbon removes dissolved organics and discolouration, and is spent after about a month. BIOMAX ceramic houses the bacteria.
• Never wash biological media in tap water, and never change it all at once. Chlorine kills the bacteria, and a wholesale change restarts the nitrogen cycle. That single mistake causes more fish deaths than any equipment failure.
• Resin pads for ammonia, nitrite and phosphate buy time. They do not fix an overstocked tank or a missed water change.

Spare parts

• Fluval sells impellers, shafts, seal rings, hoses, motor units, valves and maintenance kits individually, so a filter can be repaired rather than replaced.
• When a canister slows down or starts to rattle, work through it in order: blocked strainer, clogged foam, then the impeller. The impeller fixes most cases and costs a fraction of a motor unit.
• Part numbers look alike and do not cross between series. Check the model before ordering.

Marina betta kits

• Small decorative tanks from 2 L to 6.7 L, supplied with gravel, backgrounds and, on the 3 L kits, a water conditioner.
• None include a heater, a filter or a light. Bettas are tropical fish that need water held at 24–28°C, and most welfare guidance puts the minimum tank at around 19 litres, heated and filtered.
• One betta per tank, always. If you want a betta to do well rather than merely survive, the Fluval Spec 19 L or a Flex 34 L with a P25 heater is the setup to aim for.