Growing in coconut moss stuff with hydroponic nutrients done every 2nd/3rd day or so and water every other day. The strain is G13 labs power skunk or generic skunk, it was the "free seeds" i got when i ordered some better stuff ages ago.
nuteburn, thats what im seeing.
Could be PH or over watering, but don't worry as long as the new growth is ok. Looks like it's gonna be some tall stuff.
I am no expert, just judging by the internode spacing.
looks 2 wet , let them dry out a bit.
Rather than cutting the top off you can do Low Stress Training and just tie the top down.