Why would you want to change the media every 4-5 months, Derp?!
We usually say that you never change media, unless it is physically breaking apart. I have media that's been in continuous use for well over 15 years!
Changing media just gives the manufacturers more money and risks your fish by getting rid of your good bacteria. It doesn't matter the size of tank, amount of fish or sort of filter; keep the media! If it ever does start to disintegrate, change no more than a quarter at one time, and leave at least six weeks between replacements.