Is over filtration harmful?

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paparam

Aquarium Advice Apprentice
Joined
Jan 2, 2022
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Location
Texas
I have been toying with the idea of setting up a 45 gallon breeder tank with plants and upto 3 fancy goldfish. Before I could get into acquiring a tank I was gifted a new Fluval FX6 canister filter. I am afraid that may be too much filter capacity for a relatively small tank. Is this going to cause a problem?
 
I wouldnt say over filtration is harmful per se. I would say an fx6 for filtering 40 gallons is wasteful and the flow rates would be excessive. FX6 flow rate is rated at 925g/h which is a turnover rate of over 20 x the tanks volume per hour. While you wont actually achieve this rate and can restrict flow rate thats a lot of water going through the filter. It also holds around 6 litres of biomedia. In UK money thats going to cost about £75 to fill. You dont have to fill it i suppose, but then whats the point of the big filter?

Compare this to a 407 which is still over filtering to a significant degree. Flow rate will turnover the water just under 10x per hour, which is much more like the number you are looking for with goldfish. Each of the 4 baskets holds about 1 litre of media, you probably want 2 of them holding bio media (maybe 3). So thats about £25 to fill.

TLDR: You can probably make it work, but the only reason to do so would be because you have the filter sitting around doing nothing and you dont want to pay for another more suitably sized filter.
 
I’d have to echo what’s been said

The filtration part of it isn’t that much of a concern. Filter media capacity is a good thing in my opinion, it just lengthens the time between maintenance. Personally I think the capacity is a good thing if you want goldfish because they are generally referred to as a dirty fish!

What I’d be concerned about is the water flow rate. Like mentioned that is going to put a lot of water flow through the tank and something like a fancy goldfish is probably not going to enjoy the fast water. I’m not sure if even a 407 would be suitable as I’m running one in my 75g tank and it creates a fair bit of water movement through the tank.

If you’re set on using the fx6 (which makes sense if you’ve already got it) I would look at ways to reduce flow/turbulence in the tank. Adding lots of polishing pad material to the filter will help reduce the filters output flow. Then you want to look at how you are returning the water into the tank, you don’t want a directional nozzle as it will ‘blast’ water around the tank. You probably want to go with a spray bar to distribute the returning water over a larger area slowing the water velocity
 
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