I agree that the Eco Complete is probably raising your KH and GH. I have a fairly new tank with Eco Complete and some other substrates that are supposed to be neutral, I use nothing but RO water, and the GH and KH continue to climb.
However, I'm not upset because zero GH and zero KH are both bad things. I use RO primarily because I don't trust the local tap water, having lost a bunch of fish that way, and I want to start with the purest water I can find. If it needs minerals you can always add them later, from pure sources.