HELP! New growth leaf ends turn up. Slowed growth

[PennyK]

I have six plants in a grow room 2.5 m x 1.5 m with a 250 W HPS Growlight and a fan. The room is by a window with good air flow. I have had the light 40 cm from the plants but have moved it to 60 cm as the new growth keeps curling and growth has slowed a lot. The plants are in Cannaterra Pro soil in 4.7 litre root air pots. I water when the pot feels light. Buds are starting to form and i am giving flowering food currently. I need to solve this problem as the plants are just not growing as they should. Any help would be appreciated!

[golfnrl]

Hi PennyK...what strain are you growing? Can you post a pic of the entire plant? Type of nutrients? How much? Is that a wound from a broken stem? I don't have any experience with the soil you are using but someone on this forum will. No detail about your grow set up is too small to mention.