Fluval Flex Foam Insert 57ltr/123ltr
Water type
Freshwater + Marine
Fits
Fluval Flex 15 US Gal (57 L) Aquarium, Fluval Flex 32.5 US Gal (123 L) Aquarium
Part no.
A1375
Genuine part
Yes, genuine Fluval
Fluval Flex Foam Insert 57ltr/123ltr
Keeps the Flex's mechanical filter stage doing its job. This is the genuine Fluval foam filter block (A1375) that sits in the internal filter compartment of the Fluval Flex aquarium, trapping debris and particulate before water reaches the biological and chemical media. It fits both the Flex 15 US Gal (57 L) and Flex 32.5 US Gal (123 L) tanks, which share the same filter cartridge design.
Key features
- Genuine Fluval part – manufactured to the original specification, not a generic substitute.
- Dense mechanical foam – traps fine particulate that pre-filter sponges miss, protecting the biological media behind it.
- Direct drop-in fit – sits in the Flex filter cartridge frame with no cutting or trimming.
- Rinseable – designed to be squeezed out in old tank water and reused until it stops springing back.
Will it fit my filter?
| Aquarium | Fits this foam block |
|---|---|
| Fluval Flex 15 US Gal (57 L) | Yes |
| Fluval Flex 32.5 US Gal (123 L) | Yes |
Both tanks use the same filter cartridge frame, so this single foam block covers either size.
What's included
One replacement foam filter block. The plastic cartridge frame, carbon and biological media are not included – this listing is the foam only.
Suitable for, and not suitable for
Suitable for freshwater and marine Fluval Flex aquariums. Not suitable for other Fluval ranges – Spec, Evo and Fluval canister filters use different foam shapes.
Care and maintenance
Rinse in removed tank water – never tap water, since chlorine and chloramine will kill the bacteria colonising the foam – whenever flow noticeably slows. Replace once the foam no longer springs back after squeezing, or once it starts breaking apart. Where you can, run the old block alongside the new one for a week or two so the biological colony transfers across rather than being lost all at once.
Warranty and delivery
Covered by Fluval's standard replacement-part warranty against manufacturing defects, in addition to your rights under Australian Consumer Law. Standard freight applies.
Common questions
Does this fit the Flex 34 L?
No. The 34 L Flex uses a smaller filter cartridge – this block is sized for the 57 L and 123 L models only.
How often does it need replacing?
There's no fixed interval – it depends on bioload and stocking. Replace it once it stays compressed after a rinse rather than springing back, which is usually the clearest sign it's worn out.
Can I cut it down to fit something else?
It's sized specifically for the Flex 57 L / 123 L cartridge frame, so it isn't intended to be trimmed for other filters.
