I did a search and found some useful information but still not quite sure what is wrong
.
The grow is in soil 1/3 organic mix, 1/3 perlite, 1/3 compost.
The plant is about 5 weeks old on 18/6 with a 400w hps.
Grow cupboard measures 1700mm x 700 x 600
Ph is at 6.2 and watered with rain water.
Rh sits between 40% and 60%
Temp sits between 26 and 32C
Not sure the EC
1 dose of 1/4 strength Ionic nutrients has been given 1 week ago.
Not sure what other info you may need so here's some pics.