I have asked this before but I have a way of over thinking things and am confused. I have been mixing r/o water and the tap water I use 50/50, and I now have no idea why. The tap water parameters are ph-7.5, gh-18 dh, kh-5 dh, nitrite-0, nitrate-0 or very close to 0, ammonia-0. Is there a legitimate reason I've been doing this or can i simply use the tap water? I have a 20g with 3 platys.