Yes, I think that would mess with your cycle. I have a filter with a carbon filter media cartridge and I'm not swapping it out, I just rinse/swish it in old tank water a couple times a month to get rid of excess debris.
Carbon is very porous, so it has a while lot of surface area that you can not really see. So at first carbon will eliminate nutrients for plants, ammonia and any medicine. After about a week carbon is actually no longer useful, besides to house bacteria. Changing it every months is pretty much a giant scam, if you are gonna keep replacing you should replace it **** every week, expensive? Yeah don't replace it unless it is falling apart, and if you do seed it.
MrV, is that just a piece of sponge filter media? I promise I Googled "algae sponge" and all I found for freshwater were those used to scrape algae off of tank walls.
I have one internal filter that uses filter/carbon cartridges and I'm going to swap it out for something else as soon as I'm able (I will seed the new filter from the old). I find I prefer more control over what types of media I use and the one I have seems quirky in that it uses cartridges that are very specific and will not easily allow for adding anything else in the filter.
I'm honestly beginning to get the feeling that the OP is going to do what they feel best, so it doesn't really matter.