[EdKruzel]

Upgrading the powerhead does give more circulation and dependability over a stock pump.

Carbon should be used as a maintenance tool and not a constant filtration source.
Carbon works by both adsorption and absorption, once spent it will release excess nutrients back into the water column.
Changing every month should be safe enough provided your water doesn't contain extremely high counts of excess nutrients.

I recommend fresh carbon be used once monthly for about 3-5 days and then removed and discarded.
This will help "polish" the water giving the pristine appearance.
If left longer it will also remove good nutrients and require the hobbyist to supplement more often.