FerroVit and KH Questions

I recently purchased some FerroVit plant fertilizer and on the label it
states it should be added every fortnight.  Can anyone, perhaps a German,
tell me what a fortnight is?

I also purchased a Tetra Carbonate Hardness kit to help me monitor my DIY
CO2 injection.  It claims that the number of drops added is the amount of
dH.  On the chart it shows the value in KH.  In this case, are
these two terms synonymous?  I _do_ understand the difference between general
and carbonate (alkalinity) hardness.  Just curious about them claiming the 
reading is in dH.

Any help would be greatly appreciated.

Tyson Lee
tyson at phoenix_net