How to add dye to a loop?

[Freddie589]

So I have some deinised water, and am soon to get the rest of my kit and some dye, but do I do a full run with just the water and then add a drop to the res, power the pump to move the water, add another drop until all the water is blue? Or shall I premix it in a jug out of the case and then pour it into the loop before fist run?

Thanks
Freddie