please help new growth curling up (pics included)

[yvesNL]

these plants of a close friend of mine are displaying these symptoms, all new growth is curling and rolling upward.
The temperature in the room is defiantly not to high the lights are at a decent distance from the top of the plants and they only 400w hps, the only thing that i can think, it is is that the humidity is to low? (i know he needs a hygrometer, but his budget is completely shot.) so i suggested to put a bowl of water in the middle of his garden.
growth has come to almost a complete halt.

has anyone else had this and what wast the solution.

thanks

 

[yvesNL]

and aircon was not in use when this problem started, using it from today to keep the temperature constant as it started snowing today

 

[mike4c4]

and aircon was not in use when this problem started, using it from today to keep the temperature constant as it started snowing today

Looks like a PH, salt, or bug issue. Whats the PH? with that black plastic on the floor you might check the temp of the roots.

 

[yvesNL]

Looks like a PH, salt, or bug issue. Whats the PH? with that black plastic on the floor you might check the temp of the roots.

Thanks for the fast reply Mike, so you think it has nothing to do with the humidity? the floor temp is a bit on the low side ill get him to put some polystyrene sheets under the pots for now, and ill let him use my ph tester to test the soil run of, but last time we check it was at 6ph, he's checked the plants carefully for any bugs so don't think that's the problem. as for the salt, he lives up in the mountains far from the coast and he's used home made compost with a little sheep manure. (his veggie garden thrives on this, with no issues), other than that he uses ground water with no nutes yet

 

[mike4c4]

Thanks for the fast reply Mike, so you think it has nothing to do with the humidity? the floor temp is a bit on the low side ill get him to put some polystyrene sheets under the pots for now, and ill let him use my ph tester to test the soil run of, but last time we check it was at 6ph, he's checked the plants carefully for any bugs so don't think that's the problem. as for the salt, he lives up in the mountains far from the coast and he's used home made compost with a little sheep manure. (his veggie garden thrives on this, with no issues), other than that he uses ground water with no nutes yet

The salt buildup i was talking about is from tap water
http://www.growweedeasy.com/cannabis-symptoms-pictures