Filter upgrade suggestions

[Gypsum]

I'm currently running two Fluval U2s in a 125L Fluval Roma tank and would like to increase filtration capacity. Unfortunately, I have the tank set up in such a way that I can't fit an external filter into the cabinet it sits on (not the original one), unless the canister is less than 19cm tall. If such a thing exists, that would be nice. I would rather not stick something huge like a U3 into the tank if I can help it.

Any ideas? It would probably run alongside one of the existing U2s.

 

[Byron]

Could you explain why you intend increasing the filters? I ask because this is only a 33g (125 liter) tank and one U2 would be adequate as filtration, depending upon fish species. You cannot "over-filter" an aquarium with a benefit, provided the filter is adequate for the tank/fish.

 

[Gypsum]

According to Aq Advisor, the filtration is only satisfactory for the stocking level, and they're not cleaning the tank as well as the 307 in my other tank (I know because I'm doing the gravel cleaning!).

 

[Byron]

I will need to know the stocking level to properly respond. There is a prevalent false myth in this hobby that more or larger filters are better, but they are not--again provided the filter is adequate for the tank and the stocking is biologically balanced with the tank volume.

On the cleaning aspect, if a filter in a 125 liter tank is going to pick up solid detritus, it will have to be almost a raging torrent, and the fish will suffer. There is nothing wrong with detritus in the substrate, that is where it is supposed to accumulate. If you have plants this is the primary source of nutrients especially CO2, and if no plants, then a good clean of the substrate at each weekly water change will handle it. If the tank is overstocked, no filter is going to deal with that; filters only trap solid waste but it is still there polluting the water.

 

[AbbeysDad]

Byron is correct....there is a pervasive myth in the hobby about filtration. I wonder if this isn't fostered by manufacturers selling bigger, more expensive equipment. In any case, even well meaning hobbyists seem to echo "there's no such thing as too much filtration". BUT there is! And filters don't clean water, they just make it look clearer. As Byron pointed out, the material the filter traps decomposes and pollutes the water. And mulm on/in the substrate is fine.
I'm not really a fan of the Fluval U2 filters over a regular sponge filter. For a better filter, I'd suggest an Aquaclear 70 or a Seachem Tidal. Both are HOB filters making maintenance much easier as the filter can be serviced without shutting the filter off. And as for media, My filters are all filled with sponge material. Great mechanical and biological filtration, clean easily, and lasts forever.