I was advised to change my sponge filter every 2 months but should I completely replace it with a new one or just clean it in the tank water (out of the tank) and then put it back in? Also the filter comes with carbon and a few other materials underneath it, do they need replacing or will they be fine to leave with the filter once the sponge has been cleaned?
It's the biorb filter if this helps explain it a little more.
Just wash the sponge in tank water. Carbon isn't necessary so you can change it if you want to or replace it with an extra sponge. I believe the other media used in Biorbs is zeolite which helps absorb ammonia and that does need to be replaced as per the manufacturer's instructions as it eventually becomes saturated and stops working.