Currently have a 13.5 gal and 20 gal nanos. Just got the 20 and currently running a cycle on it now. Filtration is out until the cycle completes, but my question is when/if I need to run any carbon moving forward after the cycle. I run pretty heavy weekly water changes on the 13.5, 50%+, but want to try and keep the 20 to a 10-20% weekly change. I was looking at either a bag or carbon sponge in a caddy for the 20, but I'm curious as to if carbon is a must or not.

