How do you know if your sponge filter is working?

[JamesB]

I just decided to convert a 5 gallon aquarium to a quarantine/hospital tank after one of my other aquariums developed a case of Ich after adding a new fish. Since there were no hanging power filters (the easiest, IMHO) that provided adequate flow for the aquarium without overpowering it I decided to give these sponge things I hear so much about a go.

I purchased a Dirt Magnet Junior, their smallest sponge but that they say will handle a 10 gallon aquarium, connected it via the instructions (let's face it, it's not that complicated...) and placed it in the aquarium. What concerns me is that it doesn't seem to generate any suction whatsoever. There are bubbles rising from the tube, and when you disconnect the tube the rate at which the bubbles rise decreases drastically, a sign that the fluid dynamics should be working correctly... but placing a single flake of food on the otherwise bare aquarium bottom a half an inch away from the sponge and leaving it for half an hour results in coming back to find the flake still exactly where it was placed... just wetter.

Are the sponges not supposed to be able to move objects the mass of a flake of food or what? Everything I've read indicates that they serve as excellent biological filtration and also perform a mechanical role suitably, but I can't see it working as a mechanical filter if it's not even capable of harvesting the basic debris that needs to be collected...

Is this normal for a sponge or does it sound like I"ve hooked something up incorrectly or that there's not enough air flow?

[Ringo]

I have no clue, I have the same thing you have (only the triangle one) and I have that in my 10G hospital tank.

I've never really questioned whether the sponge filters actualy work, just kinda figured that they must work in there own way

[fish_doc]

Sponge filters are biological filters. Not mechanical. This means that it takes care of the biological side of filtration. Holding the benefical bacteria. A mechanical filter removes waste from the tank and holds it in a filter of some type. However using a bio filter does lighten the load so the waste can break down faster elsewhere in the tank.

Just remember the best way to remove waste is water changes.

[JamesB]

Packaging says bio and mechanical... but, sure. Thanks for the reply.

[Damon]

The say mechanical because the sponge will pull debris that is close to it on the sponge. It is not removed from the tank though. It holds it on itself and as it breaks down the bacteria will convert it. They dont produce enough flow to actually be effective as a mechanical filter.

[emc7]

I don't put sponges in the mechanical category at all, you can make them more mechanical by adding a strong powerhead, but the airline is just fine for biological. For a hospital tank, they are perfect, just siphon the uneaten food off the bottom and squeeze the sponge out in the waste water. If grunge comes out of the sponge, then its working.