How do I prevent reinfestation of giardia in my dog?

I just found out that my dog tested "faintly positive" for giardia this evening. He's on meds, but I'm worried because he's had a few accidents in my house lately (all on carpet) because his stomach has been upset and he's only 8 mos. old (not fully housebroken in the first place). I plan to steam clean the carpets, disinfect hard surfaces with ammonia dilutions, and to clean his toys and bedding in my washing machine that has a steam+extra hot water washing cycle ("sanitize"). My questions are 1) Isn't ammonia toxic to dogs? Will a steam cleaner do the trick instead? (2) Will shampooing/steam cleaning carpets kill it if I let the areas completely dry? (3) What's the best way to disinfect shoes?