Hi, i'm just getting the hang of all this. I need your comments on how effective sponge filters really are. I have one of those to support my othe filter in a 10g tank. I'm just wondering that if the sponge filter inside the water, doesn't all the dirt also stay inside the tank as a result? Sorry if this appears to be a dumb question. I cannot understand how sponge filters work if it stays insde the tank. Thanks in advance.

Dirt will be trapped at the sponge and you have to clean the dirt very often. It ususlly use for small fry. I would not recommend to use it for an adult fish.

Sponge filters, do indeed, just catch all the dirt and waste and hold is. As stated above, you will need to squeeze out the sponge at every water change to free the pores of the sponge from excess waste and make the water flow more freely through them.

Some power filters have sponges in them. These work well with goldies. The sponge is a great platform for beneficial bacteria to colonate - it is very porous and, as the water flows through, gives the bacteria good exposure to the ammonia/nitrite and oxygen. Squeezing it out in used fish water will remove excess wastes and preserve the beneficial bacteria of your cycle.

A "sponge filter" - one that is built on an air bubbler that uses the movement of the airbubbles up the center of the sponge tube to move water through the sponge is a great tool for fry - also mentioned above - simply because the movement of the water through the sponge is very slow and gentle. It will not harm the fry as it is sucked through. The fry can also eat the tiny particles off the surface of the sponge. A sponge filter, set up like this, however, does not give the water turnover that is necessary for proper biological filtration in a tank containing adult or larger goldfish. They are simply too messy a fish.

Adult goldfish require at least 10 times turnover of their water - far more than the average tropical fish. Gold fish are that messy. A 10 gallon tank needs a filter capable of passing all the water in the tank through the filter at least 10 times every hour - that is a filter that pumps at least 100gph. A typical sponge filter does about 5.

There are those who run the sponge filters with a powerhead - instead of the air bubbler. If this is done, it can work - particularly in a smaller tank.

I run a sponge filter with an air pump for my seriously sbd pearlscale, anything stronger just pushes her all over the tank. But, larger water changes are needed because, as Daryl said, the air pump doesn't process enough water for decent filtration, although it maintains the cycle.