<a href=showthread.php?s=&postid=10927430#post10927430 target=_blank>Originally posted</a> by AZDesertRat
RO/DI is best. Consistency if the reason, you have control of the water quality and can make sure it is the same each and every time you add it.
RO/DI removes all the VOCs, SOCs, phosphates, silicates, copper, nitrates and other things that can legally be present in drinking water but can be harmful for a reef system.