Need help odd growth

Hello! This is my first time growing and I am growing four different Fastbuds strains, Blackberry, Green Crack, Blue Dream and Grapefruit. For the most part three of the plants are coming along fine but the Blackberry has been having some odd growth right since it popped out of the soil.

I am growing inside a 4x4 grow tent using a 600w HID with a MH bulb currently about 24 inches away from the plants. I am growing them in 5 gallon smart pots using Fox Farm's Happy Frog soil mixed with 35-40% perlite. I have been giving her just 6.5 pH water only up until the last couple watering where I had added some AN Voodoo Juice (2ml/l). The last couple waterings have been about 750ml and then I let it dry out for about 2-3 days until it was dry about 1-2 inches down from the top. The lights are on 24hrs to keep the temps up, it is in my basement and it is cold here in the winter. The temp in the tent stays around 75 degrees most of the time and I struggle to keep the humidity at 40-45%. The plants are just about three weeks away from popping out of the soil.

Please take a look at these photos and let me know what you might think could be the cause and what steps I may be able to take to correct it.

I have also uploaded a pic of each of my three other plants which are under the same conditions, receiving the same water and as far as I can tell showing none of the symptoms that Blackberry is.

Thanks in advance and let me know if any more information is needed.

 

Thanks for the reply! Ok I'll just be patient and see how she turns out. As for the watering I have had so many different suggestions, on a different site, on how I should be watering at this stage I have to confess I'm totally confused. Your method lies more in the realm of how I thought it should be and will take that approach moving forward. Thanks again.