The Fluval Flex 123l build

Adzi Adam

New Member
10 Sep 2019
This is my first build thread of an already established tank the fluval flex. I have recently acquired the urge to aquascape as i like the look of a nature aquarium which serves purpose of filtration and happiness for the fish and decoration.

I stocked my fish not just one species i have gathered many different fish at the start of my hobby, now since getting into the aquascape side of things which is why i have a varied mix. I will need to accommodate these fish so it wont be a massive shoal of one species list below;

Current fish in tank
4 Gold Lazer Corydoras
6 Sunset rainbow fish
4 Goldie river ranibow fish
6 Cherry barbs
10 Amano shrimp
1 Bristlenose pleco
1 Tiger pleco
3 Gouramis
12 Neon tetra
2 Glow light tetra
6 Red stripe tetra
3 Striped loaches
6 Tuxedo platies

I have placed some plants in the tank already.

Eleocharis Acicularis
Ludwigia Repens Rubin
Cryptocoryne Wendtii Green

I am using TNC Plugs along with TNC Fertiliser.

The most annoying problem i have had with the big flex tank is the pump noise, it is very loud sounds like an air pump. This needed to be replaced so i ordered the following items.

Eheim Compact Pump 1000lph
Fluval Edge Pre Filter Sponge
Swell Fine Media Bag 10 x 12"
Seachem Matrix 1litre


I have fitted the prefilter sponge to pump as the fluval flex incorporates a back sump filtration system which gets very mucky with debris stuck at the bottom of the tank in the sump which i do gravel vac but this sponge will help the pump stay cleaner and not blast around crap from the back of the tank

Cut the foam filter sponges to allow me to fill with Seachem Matrix as the fluval provided media is very small amount which could swing my tank if i am not careful.


(I have left some of the old media in the back of the tank so it wont upset the balance)

Next task to do is get a new pipe from the pump to the outflow as the pump is floating because it is to short will be getting one this weekend which i will cut to size.


Happy with the extra flow plants are move in the tank.

Also picked up a co2 kit from co2 Art as well


Will be looking to install once we have moved house using a fire extinguisher as a co2 canister.

Current setup of tank

Was a tad cloudy even thought i have rinsed of the matrix before placing them in the filter sponges should settle down by tomorrow.

Rest of the build will be more plants and new scape once we have moved which should be in about 6 weeks time.

Adzi Adam

New Member
10 Sep 2019
Fluval should be replacing this free of charge - this is NOT normal
I had the same issue on my smaller flex i think its the chamber that causes the pump noise to be very loud however this pump is smaller in size but more powerful so the vibration noise should be less


24 Dec 2014
Bizarre :confused:

I’ve a Flex 34 at this time and have set up 5 or so (often run at home for a few days to weeks) and all have been dead quiet

Adzi Adam

New Member
10 Sep 2019
i have bought a aquael ultra max 1000. I will be removing the back panel so i can have more space and run the filtration off an external canister filter, the amount of scum that is in the back of that tank is really bad which even my heater has crud all around it.
I will take pictures once i have moved out and finished the removal.
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