Fluval FX4 Dimensions at Base?

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Aquarium Advice Apprentice
Jul 28, 2017
I'm hoping someone may be able to help with some measurements.

My 17 year old Rena/Filster XP3/XPL may need to be replaced very soon so I want to explore my options. A big concern is the physical dimensions of the filter which must fit in my current custom built-in cabinet. I think any standard canister filter will fit. I'm not conversant with current canister filte offerings but the Fluval FX4 looks like it might be an option however if I went that direction I'd need to build a new cabinet as linen is too narrow ... this is perhaps a possibility but every inch of space here is precious (apartment) clearances for traffic flow and chairs has to be factored in. My cabinet is built-in against a wall with 6" high baseboard and shoe molding.

Is the lower 6" of the Fluval FX4 narrower than 15-3/4" that Fluval lists as the width of the unit? It looks like an outboard motor connects to the canister: if the base of the canister is narrower than the top what's the narrowest front-to-back dimension at the base, motor inclusive?


  • Fluval xp4.jpg
    Fluval xp4.jpg
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Thanks for the assist Colin!

After a rigorous search I just acquired a replacement canister filter (new Oase Biomaster Thermo @ approx. 45% discount). Compared with it's predecessor the long serving XP3, the Oase is filled with the same (or slightly more) quantity of mechanical media (sponges) but 3x the quantity of biological media (Biomax from old filter and 4 liters of new Matrix) so hopefully it will also be a step up in filtration. The pre-filter stack may facilitate routine cleaning (turtles are messy so that remains to be seen; I'll still be using an in-tank pre-filter over the intake tube) and the integrated heater is a nice touch. I think it also holds a good volume of biological media compared with the FX4?

It's more compact than the Fluval FX4 & fits inside my current cabinet so I'm not time pressured(!) to take on fabrication of a new cabinet. The FX4's bottom valve (though I have no floor drain only a sink) and the accessory Fluval gravel vacuum are nice perks, the FX flow rate is fantastic, and it looks 'burly' (but not sure about durability and reliability of design on FX vs. Biomaster).

Just got it hooked up yesterday (with much less than recommended water level) and so far so good, smooth and quiet.
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