Fish getting behind the matten filter?

[megwattscreative]

Hi all,

Hope you're well! I have a 100l tank with a matten filter set up behind an egg crate moss wall. It's not siliconed to the tank, so that I can access for easy maintenance/easily rescape at a later date.

I noticed this morning that at least 1 chili rasbora and 1 pygmy corydoras had made their way behind the matten filter! There are tiny gaps on the sides that they must have slipped through. I'm totally ok with them hiding in there if they choose too, but I want to make sure they can get back into the main tank / are getting enough food. For now I've used some airline tubing wedged between the side of the tank and the egg crate/sponge to widen the gap a little bit.

Whilst I was doing this the chili slipped out, but the Cory is still chilling behind the filter. It doesn't seem stressed, but is swimming up against the glass occasionally as though looking for a way out. I do think it would be happier with the rest of the shoal.

Any ideas for better solutions than my very janky tube wedges? Id like the least intrusive options possible as I don't want to fiddle with the tank too much and stress the fish.

 

[Maf 2500]

I think long term you are going to have to think of a way to eliminate these gaps. If the tiny gaps are big enough for fish to swim through, they are big enough for water to bypass the filter. Which kind of defeats the object of having a mattenfilter. Usually the foam would be tight enough against the glass (ie oversize) for there to be no gaps at either side. Maybe you can squeeze an offcut of foam, or a piece of plastic or glass or something, down one side of the mattenfilterto make the fit tight again, if you don't want to silicone.

 

[Maf 2500]

Also, wanted to add that depending on what method you are using to return water to the main body of the tank, any fish behind the mattenfilter might be at risk. If it is an air driven lift tube then it will be no worse than a fish equivalent of a rollercoaster ride, but a powerhead or other water pump would be the fish equivalent of a meat grinder if the inlet is not screened (normally the mattenfilter itself would be the screen to keep critters out of the pump).

 

[Bradders]

I think long term you are going to have to think of a way to eliminate these gaps. If the tiny gaps are big enough for fish to swim through, they are big enough for water to bypass the filter. Which kind of defeats the object of having a mattenfilter.

Totally agree with this. In filtration terms, through - not around - is best.

 

[LMuhlen]

It isn't clear from this post, but looking at the FTS from her journal, the matten filter is very large, so the openings on the side are relatively small and probably won't affect much in terms of filtration.

That said, I would also try to prevent any gaps and make it water tight for the sake of the fishes.

 

[Bradders]

It isn't clear from this post, but looking at the FTS from her journal, the matten filter is very large, so the openings on the side are relatively small and probably won't affect much in terms of filtration.

Fair enough. I just think in terms of filtration, gaps cause the path of least resistance, and water will do its best to go around rather than through. I would try and plug it for filtration and (and you say) fish though.

 

[Maf 2500]

gaps cause the path of least resistance

This.
It is not clear how many gaps there are and how big they are. If it is only one gap just large enough for a small fish to swim through then I would suspect a relatively high percentage of the flow is going through the gap. If there are several such gaps then the flow will almost excusively be going through the gaps and the mattenfilter will not be functioning as intended.

Edit: and to be clear, I am talking about a situation where the mattenfilter sponge is established, or semi-established, and populated with bacteria and other bio-material and mulm which ceate a path of resistance to water flow. If new and naked, it would be reasonable to assume that water could flow unimpeded through the foam and the gaps would not become relevant until the filter foam is semi-blocked, at which time the gaps would become the major vector of water flow.