This week we switched our two and a half week old ducklings to a different feed. We went from Manna Pro organic non-medicated started to Purina non-medicated start-n-grow (which has pre and pro biotics). We did it gradually a 3:1 ratio for a couple of days then to half and half. Since we did this they seem to have diarrhea. How long do we give them to adjust before we try a different feed? Thanks.