Brown/copper spots random and throughout the canopy.

Looks like a small ph fluctuation. Check your runoff to see what’s going on there and gradually adjust it. But its no big deal they look super healthy. Good luck

For me it was calmag. It got locked out because I had too much phosphorus. Happened about the same time as yours too.

If this appeared after you fed them then i suspect a P or K excess. If this appeared after you didn't feed them and kept only watering i suspect K deficiency. If this appeared after you repeatedly kept feeding them without applying plain water waterings in between feedings or if you don't water untill you get run off, then i suspect a salt build up, this of course if you use mineral nutrients. If you didn't let your soil properly dry up then its probably overwatering wich also can express itself as excesses or deficiencies without it really being the case. Hope this helps you out, only you can make the right decision based on what you have done before those symptoms showed up. Good luck growmie.