Fluval AC20 Power Filter - 5-20 US Gal / 18-76 L

The Fluval AC20 Power Filter is the current generation of Fluval's hang-on power filter, for aquariums of 18 to 76 litres, with four filtration stages and a media basket laid out so each stage can be changed on its own.

Key Features

• Four stages rather than three: two mechanical, one chemical and one biological — a pre-filter sponge, a 30 PPI foam, activated carbon and BIOMAX ceramic
• CycleGuard is the important part. Each stage sits in its own space so you can change one without disturbing the others, which is what stops a filter clean from crashing the nitrogen cycle
• Patented refiltration system passes water over the media more than once for longer contact time
• Direct access to the chemical media without lifting the basket out, so a carbon change does not mean a dripping mess
• Pre-filter intake strainer keeps algae strands and debris away from the impeller
• Re-engineered rotor for smoother running, and a moulded rim connection that makes levelling easier
• All media included. Made in Italy
• 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

Setting It Up

• Hang it on the back rim, fill the chamber with tank water to prime it, then switch on. Do not run it dry
• 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
• Set the flow control low at first and work up. It is easier to judge what the fish are comfortable with than to guess
• No filter is silent. Most of the noise people complain about is air trapped in the impeller housing or a unit that is not sitting level

Maintenance

• Change one stage at a time. That is what CycleGuard is for, and it is the single biggest thing people get wrong with filters
• Rinse mechanical foam in a bucket of old tank water rather than under the tap
• 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
• Carbon monthly, foam rinsed every couple of weeks, BIOMAX partially replaced every few months
• Unplug anything electrical before putting your hands in the tank
• A liquid test kit for ammonia, nitrite and nitrate tells you more about a tank than anything you can see

Good To Know

• Fluval lists this as the direct replacement for the AquaClear 20. If you are replacing an old unit, this is the current equivalent
• The main practical gain over the older AquaClear is the separated media stages. Being able to change carbon without touching the bacteria is worth more than it sounds
• Hang-on filters need the water level kept up, or the return splashes and gases off CO2 in a planted tank
• The waterfall return is too much current for a betta or a fancy goldfish. Turn the flow down or baffle the outlet
• Most tanks want 20–30% of the water changed weekly, with the replacement dechlorinated and matched for temperature