Filter replacement frequency

[Klyph]

I’ve had a 32G bio cube for about four months now, and haven’t yet replaced the filter in the back. What’s the traditional frequency for doing so?

I thought I had read somewhere that replacing the filter could remove beneficial biomatter, and could actually be detrimental to the ecosystem. Thoughts?

 

[AdamNC]

I clean my filters sponges every week. Otherwise they build up too much detritus and raise Po4.