Clean the filter when it's been running 6 weeks by very gently squeezing it in old tank water to remove any goo that's built up on the sponge.
The bacteria live in the biofilm on the surface of all those bubbles in the sponge.
Sponges ony need changing when they go into holes or won't go back into shape after squeezing. They last for years. When it does eventually fall apart, cut the sponge in half - not in the direction of water flow, across it or the water will just go straight through the gap - and replace half, then a month later, the other half.
If you do change the filter, put the current filter's sponge in the new filter. You can chop it up to make it fit.
The bacteria live in the biofilm on the surface of all those bubbles in the sponge.
Sponges ony need changing when they go into holes or won't go back into shape after squeezing. They last for years. When it does eventually fall apart, cut the sponge in half - not in the direction of water flow, across it or the water will just go straight through the gap - and replace half, then a month later, the other half.
If you do change the filter, put the current filter's sponge in the new filter. You can chop it up to make it fit.