I just got some EcoPure, and it arrived in black bottles. How do I know how much liquid is in them after I start to use one? I also custom mix and refill the 3mLs from a 15mL. With the white bottles I use a small flashlight against the side of the bottle to see the liquid level. The black ones also seem to be smaller(100 drops in white, 85 in black)That's OK as long as I'm getting 3mLs of EcoPure.