Is it necessary to mix an entire bottle of TF-5 in one go? For example, if I get the one liter bottle of concentrate, do I need to mix the whole thing to four liters of working solution, or can I just mix, say, half of it to get two liters, and mix the other half later? This is with an eye to both maximizing shelf life, and simply not storing a whole gallon or more of working fix at one time. I know TF-4 concentrate has a tendency to settle out but it looks like TF-5 is more homogenous?