Yes, your lfs
will tell you replacing the cartridges monthly (or weekly or whatever) is necessary. Its not & it will throw your tank back into a cycle when you lose all the good bacteria. If they are carbon filters, you can dump out the carbon & stuff them with filter floss (polyfill) or you can replace it with a filter foam insert (sponge) instead. Your tank is now cycling again. Do you have an API test kit?