Rank #1 in Best Aquarium Filter 2026: Turnover Is the Only Number
Fluval U2 Internal Aquarium Filter, Up to 110 Litres, 400 L/H Adjustable
Price and rating as shown on Amazon when we collected them. Both change.
The Fluval U2 is the most-reviewed aquarium filter here: 8,108 ratings at 4.2 stars for £36.00, with adjustable flow up to 400 litres an hour, three stages of filtration and a stated tank size of 110 litres.
It takes first place because it is the only filter here with both numbers you need — the flow and the tank size — and three times the evidence of anything else. At 400 L/H for a 110-litre tank it runs at 3.6 turnovers an hour, the bottom of the recommended range.
How those 8,108 ratings break down
An average hides its own shape. This is the spread behind the 4.2 stars.
Specification
Exactly as published on the Amazon listing, field for field.
| Maximum flow | 400 litres per hour |
|---|---|
| Stated tank size | Up to 110 litres |
| Turnover at 110L | 3.6 times an hour |
| Filtration | Three stages with BioMax |
| Ratings | 4.2 from 8,108 |
| Price | £36.00 |
What buyers actually say
Quoted from customer reviews on Amazon
Verified purchase“Brought to replace a failing one. I find these last a few years and then start failing. I like this filter, it is quiet and does the job well. Needs cleaning about every 2 weeks in my 100L tank.”
Verified purchase“Really good filter. I've been having it for years now and honestly im really happy with it. Im using it in a 90L tank, works great, not too strong water flow, which is good for my lazy fish. Its easy to assemble and clean, quiet (especially if fully submerged) and not too heavy. There's no smell from it if cleaned properly”
What it is up against
The rivals it was ranked against in Best Aquarium Filter 2026: Turnover Is the Only Number.
Questions people ask
What tank size is it for?
Up to 110 litres, which at 400 L/H is 3.6 turnovers an hour: fine for a 60-litre tank at 6.7, marginal at the top of its range.
What is the 4-6 times rule?
The common advice that a filter should turn a tank's volume over four to six times an hour. No listing here states it, which is why you have to do the division.
Is the flow adjustable?
Yes, which matters in a planted tank or for fish that dislike current.
Can I use it in a marine tank?
The listing covers freshwater, marine and reptile use.
Why is it first?
Because it publishes both numbers, has three times the reviews of anything else here, and the brand means spares exist.
How many ratings does it have?
8108 at the time of collection, averaging 4.2 stars, with 66 per cent five-star and 11 per cent one-star.
Comments
Reader comments are not checked against the manufacturer's claims above.
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