My Seedlings & Question

I have recently germinated my seeds and they are in 1" rockwool cubes at the minute, Im going to be using a drip feed hydro system.

The seedlings are on average 2 and a half inches tall with just the (baby) leaves at the top.

At what point should I start with nutrients in the water that i apply to the small rockwool cubes or should I just keep it pure water for now?

I gave the cubes there second watering today as they had dried out since the initial watering when i placed the germinated seeds into them, also one root has now made it to the bottom of each cube.

Any help is appreciated

Leave it another week i done something simlar! wait until there transplanted

Thanks for the help, So should I leave them another week before putting them into the 4inch cubes and then into pots with the expanding clay pellets?