i using red sea additives, ABCD + alk + Ca, have mag but not using. So total would need 6 dosing heads. My 2 cents is get as many heads as ur budget and space allows, u may never know when u want to start dosing other elements. I have not used all for reef b4 so cant comment but my opinion is better to split the dosing as each element consumption might be different, as my tank rarely consume magnesium. Sent from Singapore Reef Club mobile app