Re: Want to build a carbon filter...
You can buy them online at water filtration sites but if you want to buy it locally then you can buy it at an aquarium store or any fish related store you can find. They usually sell it in 5 lb bags.
1) Reverse osmosis
2) Get a reverse osmosis system but make sure you add a calcite filter. It adds calcium to the water.
3) I don't think it's necessary and wouldn't recommend it. Instead, use a calcite filter.