purple is is recomended for new aquariums only with no corals. as it says so on the bottle. but yes, it does increase calcium,alk,iodine and a few other things.
i used this product and somehow missed the the part where it says "for new aquariums". Yes it did work good on the coraline growth part. but they dont tell you how it will kill yer clams. i noticed my trids were starting to look like poo after a few weeks of using it. it was too late. i stoped using it because it hurts filter feeders.they dont naturaly eat chunks of minerals everyday for breakfast. so use with caution everybody!