PurAmino formula

My son has been on PurAmino for about a week now for protein allergies and reflux.. we also add rice cereal to his bottles for the reflux as well.. his poop is almost black (dark hunter green) and sticky.. he's also sleeping A LOT! Is this normal? Or has anyone else experienced this? Before this formula he was breastfed and supplemented with Alimentum rtf but was still testing positive for blood in his stool so we switched to the higher hypoallergenic formula..

And too, with PurAmino the directions say one scoop per one ounce of water.. every formula I've ever seen has been one scoop per two ounces of water..