The frogger is a silver/zinc system. Siver is bacteriostatic but has a very slow kill time. I have no idea what zinc does in the water but I suspect is act similarly as copper (anyone out there know for sure?)
You might want to read this thread about 'minerals' (a nice name for metals) in the water
http://www.poolforum.com/pf2/showthread.php?t=98