Please help. need advice

.hydroponic drip system.600w hortilux (x2).rockwool medium.my clones are well rooted in rockwool and just about 3 weeks old.they are now in 3" cubes and seem to have adjusted to the lighting. the leaves on most of the clones are turning light green almost yellowish in colour. i was wondering when is a good time to introduce some nutes. i just added some today about 330 ppm, hope im not jumping the gun. any help would be appreciated thank you.

Sounds good.

In another week drain the rez and bring them up to 600.

It can be hard to judge the color with the HID light on
so it is best to take a look under regular light.

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thank you for answering my question..