Sponge Filters

Do sponge filters stop working after a while or might something have happened to mine??

I have 5 filters running, my original ones bubble stream was getting worse and worse, so I started to think it was the airline, but I swapped them about, and one that was working fine with a good stream of bubbles, with the old filter on is pathetic, so I imagine it can't be functioning as well as it should??

Basically I've ruled out the pump and airlines, so it must be the filter, where are the bubbles going if they're not going where they should?? Has the sponge stopped making contact somewhere it should be?? Its about 3/4 years old, do they have a shelf life? do I just need a new sponge, or should I replace the whole thing, bearing in mind they're not expensive??

Sponge used in filters is "open foam" meaning that one bubble leads to the next. Over time these cells can become clogged with dirt to the point where it's nigh on impossible to clean them, when this happens the water flow through them is significantly affected, that is to say, for the same amount of bubbles going up the uplift tube, less water will be drawn through the sponge, when compared to a newish, unclogged one.

However, whether you have a new sponge, old sponge, no sponge or block of concrete on the filter, that shouldn't have any effect on the amount of bubbles going up the uplift. If the flow of bubbles is feeble, that could be down to a blocked airstone, blocked or kinked airline pipe (sometimes a calcium deposit can form in the very end of an airline, and soot & dust deposits can sometimes block gang valves.) If you're using a single air pump to feed two, or more, airlines, through T pieces or gang valves, the air will tend to follow the easiest route, the deeper the tank, the harder it is for the pump to pump to the bottom, restricting faster running airlines will force more through the slower running ones.

where are the bubbles going if they're not going where they should??

It could be that there's a leak and the air's escaping, but the amount of air being delivered is not a fixed amount. When you suck on a straw, it's easier to draw water up it, than a thick milkshake. You put more effort in and get less shake. The pump just produces a fixed amount of effort, so delivers less air if the restriction is greater.

Hi Rob, thanks for the reply, it was the lack of bubbles that was confusing me, so now the airline has got a new(seeded) filter on it and its fine, I put the old sponge on the airline that I seeded the new one, and I have a pathetic stream again, I guess a tube must be blocked somewhere inside the filter then, maybe I'll just chuck it out and start again

Well never liking throwing things away, I decided to take the filter apart, couldn't see anything wrong, so I put it back together. and guess what Its fine!! back to a great stream of bubbles It had to be something simple after all!! I'll let it mature a bit and then put it back in a fry tank.

Ok another question on sponge filters!! I have 4 in a row (different tanks) all with a good stream of bubbles (at last), one of the sponges has what I can only describe as a film over it, I tried taking it out the other day and gave it a squeeze but it doesn't seem to have improved it too much if at all, how vigorous a "clean" (in tank water of course) can I give it before it loses its good bacteria?? I'm feeling as it looks clogged its not working as best it should?? water seems ok at the moment, but the fish are getting bigger. I guess ideally I should have another seeding somewhere, so I can swap one out. (I'll get on to it in the week), but thats gonna take a few weeks.

The more vigorously you rinse the sponge, the more bacteria you lose. As you say, having an extra filter running somewhere to swap out when required, is a good thing to do.
Otherwise, depending on the design of the filter/sponge you may be able to cut the old one in half, and then partially slip on the new one for a few weeks, before finally discarding the old one.