I recomend doing 2 every week. Say all the guppies you got had ich from the store, and you got 4 over a two day span not suspecting anything. Next morning all 4 are dead due to ich, 2 every week: If 2 of your fish have ich then 2 will die. then you get more the next week, last weeks stock of...
Lol i am mr.kitty your tour guide! All i have around here are marine stores, petsmarts and petcos, but they do get in trouble for animal cruelty, so they try to keep the fish dicent! :)