Should I be adding KH when using Tom's non CO2 method?

I'm running my newly setup 55G tank (setup a week and a half ago) using Tom's non CO2 method as described here: http://www.barrreport.com/articles/433-non-co2-methods.html

However, I just did a test of my water hardness and the KH is very low (went from 80ppm in the tap to 20ppm in the tank). I have two large pieces of drift wood in the tank so I'm not sure if they are partially to blame (does peat and drift wood affect the GH or KH or both?), however, the article states that the plants will also use up the KH to get CO2 from it. Since my levels are so low should I be adding KH? If so, anyone have any rough recommendations about how much to add on a weekly basis? Or in other words how much KH do plants use up in a week? Sort of a KH component of the Estimative Index.

Thanks,
Harry

P.S. I have very very little evaporation on this tank so adding normal tap water to replenish evaporated water and thus replenish the KH might not work (unless the plants user very very little of the KH and the huge KH drop in my tank is purely due to the driftwood). Thanks again.