If you are planning to use carbon dosing to reduce high levels of nitrates and/or phosphates, please keep in mind you need to start off slowly and at a very low level. Making quick and drastic changes to your nitrate levels through all/any forms of carbon dosing will cause your water parameters to become at least somewhat unstable. Take it very slow to begin with allowing your system to slowly adjust over time. You have to always keep in mind, only bad things will happen fast in this hobby.
More information about carbon dosing can be found in the below article:
And a few other articles about carbon dosing