Fluval Flex and Fluval Spec Accessories: Media Baskets, Spray Bars, and What Actually Fits Today

Fluval Flex and Fluval Spec are two lines of all in one aquarium kits, each with a filter built right into the tank instead of hanging on the back. Both are some of the most modified tanks in the whole hobby, and third party sellers do steady business making media baskets, spray bars, intake covers, and lid props for them.

TankRig now sells a media basket for five of these tanks: the Flex 9, Flex 15, Flex 32.5, Spec III, and Spec V. Fluval has never published the inside measurements of a Flex or Spec filter chamber, so we designed each basket to the best measurements we could find, not a guess. This guide covers what makes Flex and Spec different, what accessories people want most, and how our own baskets are designed to fit.

Fluval Flex vs Fluval Spec: what is actually different about the filter chamber

Flex and Spec are two different tank shapes with two different built-in filters. Neither one is just a small or large version of the other.

The Flex line comes in three sizes: 9 gallon, 15 gallon, and 32.5 gallon. Each one has a rear filter section most sellers split into a Chamber 1 and a Chamber 2, plus a separate pump chamber. The Spec line is smaller and sits on a desktop: Spec III at 2.6 gallon and Spec V at 5 gallon, each with its own compact filter compartment built into the tank body. A third tank, the Evo 13.5 gallon, gets modified by many of the same sellers and is worth knowing about too. It is the same physical tank sold under two names, Evo for freshwater and Sea Evo XII for saltwater, depending on where you buy it.

Fluval and its retailers publish the outside size of every one of these tanks. Nobody publishes the inside size of the filter chamber, the number that actually decides whether a printed basket or cover fits. That gap is why this guide can tell you a tank's footprint but cannot tell you a chamber size yet.

The most requested Flex accessories (spray bar, media basket, intake cover, lid prop)

Four kinds of accessories come up again and again for Flex and Spec tanks.

• Media baskets. A basket or shelf that sits inside the tank's own filter chamber and holds loose or bagged media, instead of relying only on the stock cartridge.
• Spray bars and flow diffusers. A part that spreads the filter's return flow into a wider, gentler stream instead of one hard jet aimed at the glass.
• Intake covers. A cover over the tank's built-in intake grate, meant to help keep shrimp and fry away from the pump.
• Lid props. A small prop or riser that holds the hinged lid open a few inches, for feeding or for running a cord or airline through the gap.

Why so many Etsy sellers specialize in just this one tank family

Flex and Spec tanks pack a full filter into a small, closed off space. That space cannot be resized or swapped for a bigger one, so an owner who wants different media, gentler flow, or shrimp safe intakes has to modify what is already there instead of buying a different filter.

That is exactly the kind of problem 3D printing is good at. A stock filter chamber is one fixed shape, but a printed part can be shaped to match it and still leave room to change how media sits or how water flows out. That is likely why this is one of the most active print-to-order categories in the whole aquarium hobby, not a small corner of it. Several independent sellers build their entire shop around Flex and Spec accessories alone, and they do real, repeat business doing it.

We are not first to notice this. We are just not willing to guess at a fit to get there faster.

What TankRig fits for Fluval today, and what is still coming

We now sell a media basket for the Flex 9, Flex 15, Flex 32.5, Spec III, and Spec V. We also sell two media baskets for the Evo 13.5, one for each chamber, even though this guide is mainly about Flex and Spec. Fluval has never published chamber dimensions, and we could not find anyone else who has either, so we designed each basket to the best measurements we could find, not a caliper reading off a physical tank.

That is the honest trade we are making. A basket sized this way is designed to fit, not verified to fit. Tank molds vary, so check the fit in your own tank before you rely on it. We also sized each basket a little small on purpose, so a loose fit is more likely than a jam.

Every basket is PETG, the material aquarium keepers have used submerged for years, and made in the USA. Rinse any new part in clean water before it goes in your tank, the same as you would any other part. Spray bars, intake covers, and lid props for Flex and Spec are not on the list yet. Media baskets came first.

Frequently asked questions