Originally Posted by miles
The most compelling reason I've heard for not using carbon is that it can leech phosphates into the water (is this true??).
It is possible, yes. Probable, no. Base material used for conversion to carbon is sometimes 'activated' with phosphoric acid. If you buy quality brands made for aquarium use, I think this very unlikely. Also the amount leeched would be extremely small.
Like most things that go into an aquarium, it is often best practice to use things only when you believe there is a compelling reason to use them. And so it is for carbon.