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Filtration for 125l tank advice please

L

lee324

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Joined
29 Apr 2025
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Location
Wales
Hi, my son has a 125l jewel tank in his room, it's not live planted it has very course gravel populated with 7 goldfish.

The filter that's come with it doesn't seem powerful enough and I've also got a lot of black & green algae. To keep it in a good state I have to strip to tank at least once a month which I know isn't how it should be, I have been looking online for better filtration and was hoping someone could offer some advice if what I've chosen would be suitable.

Fluval 207 external filter with phosphate filter pads

Fluval UBC inline

Fluval spray bar

Pen plax under gravel filter

And a power head

Basically I was thinking of attaching the suction side of external filter to one up drift tube of gravel filter and on the opposite a power head as under the gravel is especially dirty.

Spray bar for surface agitation

Would this be ok to set up as I don't want to waste the money on items that's going to be a waste of time also cannot be too loud because of where the tank is

Thank you
 
Just to be clear, are you saying you have an Under Gravel Filter at the moment?
 
lee324 said:
To keep it in a good state I have to strip to tank at least once a month which I know isn't how it should be,
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Also, can you describe what you mean by this. i.e. what happens for you to strip it down, and what does strip it down mean exactly?
 
Got it - sorry to be a pain, but can you send a full tank show so we can see what you are looking at? Just gives us a view of the environment, size of fish etc...
 
lee324 said:
Hi, my son has a 125l jewel tank in his room, it's not live planted it has very course gravel populated with 7 goldfish.

The filter that's come with it doesn't seem powerful enough and I've also got a lot of black & green algae. ...
Click to expand...
First of all: your Juwel filter is most likely exactly the filter you need. I use several Juwel filters and they all work perfectly. Even with a fairly high stocking. Oxygen is essential for the decomposition of organic material in the aquarium. There should be sufficient surface agitation for this. And your Juwel filter can definitely provide this. If too much organic residue accumulates in the aquarium, then I suspect that too much food is being fed. Possibly with sub-optimal food. Goldfish definitely need a certain amount of carbohydrates, but not necessarily in the form of wheat flour.
To improve your aquarium, it would be essential to know what is being fed, how often and how much. How big are the fish? Is there a picture of the entire tank? Coarse gravel is perfectly suitable for goldfish. As long as the fish can't swallow any stones, this is a good choice. How is your filter equipped and how is the outlet aligned? Which pump is in your filter?
Some floating plants such as hornwort and duckweed can help to improve the biology in the aquarium. Goldfish also like to eat duckweed. It is a good supplementary food.
 
Thank you, the pump is ecoflow 500 with I think 3 sponge

feeding is currently every other day and that is aquarian flakes. I can get a picture when I'm home tonight

I have an API 400 air pump with two long stones spanning the rear of the tank and the filter outlet is angled to create as much surface agitation as possible

The fish aren't big probably 4cm possibly 5cm
 
lee324 said:
Thank you, the pump is ecoflow 500 with I think 3 sponge ..

The fish aren't big probably 4cm possibly 5cm
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As long as the sponges are not clogged up, they will do their work. There should be no problems with seven small goldfish. Another filter is definitely not necessary. The eccoflow Pump 500 is also sufficient.
 
I've not kept goldfish but as I understand they are extremely messy fish. Do you have a larger tank to move them to once they've grow? Looking at your filter, it's rated at 500lph so will probably be nearer half that after overheads/restrictions. I can't find dimensions but it doesn't appear to have a much volume for biological filtration. If it was me I would have upgraded the filter but I do almost always go over required spec for my hardware and I'm not experienced in keeping these fish. If what @Teleos says is correct and the filter isn't an issue, then I would looking at food/feeding, I've never tried flake food as I always read it was inferior to a pellet food? Sure I read it was due to binders or something of the like? Are you using a good quality food?
 
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