Carbon related questions

[importracer]

I know you must remove carbon before medicating, because it neutralizes the medication.

Here are a few other carbon questions.

1) does carbon "go bad" or need to be replaced? if so, how often?
2) does carbon only effect medication, or does it effect everything else too? (Stress coat, prime, plant food like iron and flourish etc.)
3) does it need to be completely removed from the tank or can you just drop the filter in the tank to keep the bio alive?
4) When treating, how long should the carbon be left out?

Personally, I stopped using carbon 10 years a go.......I have been using carbon sonce the early 80's..........With todays' filtration options, and the DIY techniques, plus 50% water changes every week, tanks stay perfectly clean.............