It is fine. Lots of people dilute it one to one so you could consider that every liter you start with from your mix needs to have 2/3ds liter water added to make it one to one. Or if you tend to use only one or two types of film then just run a test and push your normal time a little bit to see where it needs to be and then just use it like that.
Dennis
PS that 2/3ds liter water is quick math in my head which is fallible. I figured that all 6 liters you have mixed need an equal part of 4 more liters water to make it 1-1.