The Fluval Flex 123L takes the Fluval Foam Filter Block for Flex Aquarium Kit (57 L and 123 L) (part A1375) as its filter media; Australian sellers list it from A$13.88 as of 30 October 2026. Fitment confirmed against the manufacturer's compatibility list.
Your aquarium filter
Fluval Flex 123L
Aquarium filter
Confirmed against Fluval's listConfirmed against Fluval's own compatibility list
Not yours? Change
Takes the A1375 filter media
Foam Filter Block for Flex Aquarium Kit (57 L and 123 L) · check the code printed on your old filter before ordering.
Your aquarium filter
Aquarium filter
Confirmed against Fluval's listConfirmed against Fluval's own compatibility list
Takes the A1375
Filter media · check the code on your old filter.
Other Fluval aquarium filters that take the A1375
GenuineGenuine Fluval
$13.88
Aquarium Spare Parts · 30 OctLowest genuine · Aquarium Spare Parts · checked 30 Oct
CompatibleCompatible option
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No compatible seller tracked yetNo compatible seller tracked yet
Genuine: made by Fluval. Compatible: another brand.Genuine is made by Fluval. Compatible is made by another brand. Check the seller's page for the size and models it fits.
Lowest price · $13.88
Aquarium Spare Parts. Every seller we track is listed below. Some links earn us a commission. Some seller links earn us a commission, at no extra cost to you.
Other parts this aquarium filter takes
- Fluval BIOMAX for Spec/Evo/Flex/Betta Aquarium Kit, 60 gOpen Aquarium Spare Parts$7.88
The biological media. Separate from the filter media. Reduces ammonia and nitrite, via the bacteria living on it (biological media). Replace every 3 months.
- Fluval Carbon for Spec/Evo/Flex Aquarium Kit, 45 g, 3-PackOpen Aquarium Spare Parts$2.63 each · 3-pack $7.88
The carbon filter. Separate from the filter media. Reduces heavy metals, odours, discolouration and pollutants (Fluval wording for its kit carbon). Replace every month.
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AUD, before delivery. Each price shows when it was checked.
Opens Aquarium Spare Parts in a new tab. Their page is the source of truth for price, delivery and returns.
How long it lasts
Replace it as the filter's manual says; Fluval gives no set interval for this part.
How to change the filter media in your Fluval Flex 123L
Watch the guide or follow the steps.
No clear video for this part yet. The steps cover it.
- 1Unplug the pump and lift off the cover of the filter compartment at the back of the tank.
- 2Lift the media (foam block, carbon and BIOMAX) out of the filter chambers.
- 3Rinse the foam block in water from the aquarium; Fluval says to rinse BIOMAX monthly in aquarium water.
- 4Fit the new foam filter block where the old media sat. Fluval says not to replace all filter media at the same time.
- 5Put the media back in the same chambers, refit the cover and plug the pump back in.
Every number this part goes by
- Retail name:
- A-1375
- Retail name:
- A1375
Sellers list any of these; they are the same part.
About your Fluval Flex 123L
Fluval aquarium filter — Flex aquarium kit (rear filter). Its filter media is the Foam Filter Block for Flex Aquarium Kit (57 L and 123 L), part A1375.
Also in this aquarium filter: Fluval BIOMAX for Spec/Evo/Flex/Betta Aquarium Kit, 60 g (every 3 months), Fluval Carbon for Spec/Evo/Flex Aquarium Kit, 45 g, 3-Pack (every month).
Where the model number is: The model is on the filter's lid, motor head or a label on its side (Fluval 307, Eheim Classic 2215). For a tank with a built-in filter, use the tank's name.
Common questions
- Which filter media fits the Fluval Flex 123L?
- The Fluval Flex 123L takes the Fluval Foam Filter Block for Flex Aquarium Kit (57 L and 123 L) (part A1375).
- Where can I buy the A1375 in Australia?
- We track 1 Australian seller for the A1375; the lowest listed price when we last checked was A$13.88 at Aquarium Spare Parts. Prices are re-checked daily and dated on this page.
- How do I fit the A1375 in a Fluval Flex 123L?
- No tools, a few minutes: 5 steps, listed on this page with the replacement video where the maker has one.
- What happens if I don't change it?
- Spent carbon stops removing odours and discolouration, and clogged pads slow the flow, so the filter moves less water through the tank.
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