Perhaps you are right and temp. as low as 16c may be harmful. Anyway, now they don't seem to have a problem with the low temp. at night. The soil I used was without any nutrients, afaik. At least pH in the soil seemed normal.
I'm very curious about how the plants will like the new 150w HPS instead of 400w, because, now the average temp. when light is on, is approx. 24-25c.

By the way, not too long ago I got a good deal on cannabisseeds.com, 12 feminized super silver haze seeds for 20$, which is a bargain imo. Actually, I was a bit surprised, because i've seen quite a lot of people complaining about that seeds company. I got my seeds after about one week I think.