Ive just read in my filters maintenance book the carbon filter should be changed every 3-6 weeks?? does that mean I have to start the cycle again each time?
If the carbon makes up less than a quarter of the total media, you can replace it without losing too many bacteria. However, you don't need to run carbon all the time, so you'd be better off replacing it with something that will last longer; ceramic rings or coarse sponge make very good biomedia.