← Fluval Flex 9 (34L) · All nano return pumps
Best pumps for the Fluval Flex 9 (34L)
Target a return pump that turns over the display volume roughly 5 times per hour, with 4 to 8 times per hour being acceptable. If the pump has no published flow-vs-head curve, derate the rated flow by about 25% to account for head loss from the return line. DC pumps are worth considering on nano tanks because they're throttleable, letting you dial back flow if the rated output is higher than needed.
The Fluval Flex 9 is a 9-gallon (34L) total, roughly 7.5-gallon display nano AIO with a 14 × 13.4 in bounding footprint and a signature curved front glass. It ships with an integrated 7500K white + RGB LED (~5.26W) on Fluval's FLEXPad remote, suited to low-to-mid-light setups rather than demanding corals. The hidden rear sump's intake-chamber depth is the binding constraint for an aftermarket pump or nano skimmer, roughly 2.1 in front-to-back based on inTank media-basket fitment (community-derived, since Fluval publishes no chamber dims). The stock return pump moves about 92 GPH.
MightyJet Desktop DC (326 GPH) $146.00
- DC pump — dial flow to taste
- strong: ~32.6× turnover — fine if controllable/throttled
- 3.7×2.5" footprint may not fit the ~3.875×2.125" chamber (community dims — verify)
All pumps compared
| Pump | Max flow | Type | Price | Verdict |
| MightyJet Desktop DC (326 GPH) Innovative Marine | 326 gph | DC | $146.00 | Top pick |
| MightyJet Midsize DC (538 GPH) Innovative Marine | 538 gph | DC | $159.00 | Likely — verify fit |
| VarioS-2 Controllable DC Reef Octopus | 792 gph | DC | $311.84 | Likely — verify fit |
| Sicce Syncra Nano Sicce | 110 gph | AC | $34.99 | Too strong (AC) |
| EHEIM compactON 600 EHEIM | 159 gph | AC | — | Too strong (AC) |
| Tunze Silence 1073.008 Tunze | 210 gph | AC | $54.99 | Too strong (AC) |
| Sicce Syncra Silent 1.0 Sicce | 251 gph | AC | $69.99 | Too strong (AC) |
| IceCap EVO 1000 IceCap | 315 gph | AC | $40.01 | Too strong (AC) |
FAQ
How big a return pump do I need for a 10-gallon AIO?
Aim for roughly 50 GPH of actual flow at head, which is 5× the 10-gallon display volume. If the pump has no head curve, take the rated GPH and reduce it by about 25% to estimate real-world output, then pick a pump whose derated flow lands in the 40-80 GPH range.
What does 'derating for head loss' mean and why does it matter?
Head loss is the flow reduction caused by the pump pushing water upward and through tubing back to the display. A pump rated at 200 GPH in open water may only deliver 150 GPH or less at your actual return height. Without a published flow-vs-head curve, a 25% derating is a reasonable approximation.
Is a DC return pump worth it on a small tank?
Often yes. DC pumps let you throttle flow down if the rated output is too strong for your nano, and they typically run quieter and cooler than AC pumps. The tradeoff is higher upfront cost, but the controllability is genuinely useful on tanks where a few GPH can make a noticeable difference.