in the test kit. what does hardenss.
the carbon in my tank.
and what level shoud it be at
Not exactly sure what you're asking about with the carbon. The page says the kit tests calcium, carbonate hardness (KH), phosphate and nitrate.
You can read about kH here, about halfway through the page:
http://www.drhelm.com/aquarium/chemistry.html
They explain it quite well there.
Carbon can absorb chemicals within your aquarium. Carbon media almost always contains phosphates. Some people use carbon all the time and some use it just to remove chemicals. It usually has to be changed after 2 weeks, or up to a month depending on which kind you buy. Usually if you medicate your tank, it's recommended to take the carbon out (so it doesn't absorb the medicine).