From FrugalReef

Activated carbon's properties come more from it's physical properties than from it's reactive properties. Active carbon is special because it has a very large surface area with which to absorb. One gram of activated carbon often has double the surface area of a tennis court. This large surface area is also readily colonized by bacteria.

Contents 1 Things active carbon removes well 2 Things it removes that you may want to keep 3 Things active carbon does not remove well 4 Problems to look out for 5 See Also

[edit] Things active carbon removes well

• Chlorine
• Sediment
• Organic Compounds
• "yellowing" of aquarium water

[edit] Things it removes that you may want to keep

• Iodine
• Most Medicines

[edit] Things active carbon does not remove well

• Minerals
• Ammonia

[edit] Problems to look out for

• All activated carbon leeches phosphate. Some brands leach more than others. To compare brands, place a teaspoon of carbon in a gallon of water and test for phosphate after half an hour.
• Possible absorption of trace elements

[edit] See Also

• http://www.hallman.org/filter/gac.html
• http://www.netpets.org/fish/reference/freshref/carbmeth.html