leaf turn dark and curling down

Thank you all for the answer. It’s is because of lack of water.I got my self a soil hygrometer.bottom half of my pot was bone dry. I up my water to 2 liter since I had a big pot I see some massive change to the plant it was stretching more than previous watering and look happy.but unfortunately I haven’t cut down the fish mix and bio grow together.still some slight purple and curl down leaf at the tip.for next watering i will cut down both of the nutes. Cheers!

Looks like under or over water to me. How well is your medium draining? Doesn't look like the slight over nuke could cause this. My 2 cents.

Don't use fish mix and bio grow together.they both include high N and can easily create N toxicity.I had it before with biobizz.Cutting one off solves the problem,i would cut off both for a week in this situation to make sure new growth don't have tips pointing down. Your plant has a dark tint which is the result of excessive nitrogen feeding but droopy look is probably because of low stress training.plants sensitive to lst in early stage always look like this.it is not a problem,leaves will find the right angle in a few days if you stop bending now