Plants keep dyiing,please help

[Ace]

I've had a total of about 4-5 plants die.I think there are only two reasons why they are dying but I want to make sure.Right now I have a large pot filled with clay.I think this could be one of the problems.I live in India so it's hard to find good quality soil and fertilizer,and I don't think the clay has enough nutrients for the plant.The other reason why I think they are dying is because there's not enough air circulation where they're at.They are being placed right next to a window which is only opened during the day,and closed at night(for mosquito reasons).Do you think one of these reasons are why my plants are dying?Also,they usually get about 16-18 hours of light a day.From 8a.m. to 6p.m. the sun provides the light,then I have a 4 foot flouresant(sp?) light on when the sun goes down.I've tried adding sugar when watering and that seems to help them from dying so far,but my one plant thats still alive just refuses to grow over 5 inches.Here pretty soon I'm going all out and buying everything I need to grow indoors from the internet,but until then I want my plants to grow nicely where they are.

Thanks for any help you can give me

 

[Lionpenn]

From what I understand,clay sucks. No drainage or anything good. As far as light I grow inside and only use light 18 hours a day. Pot only processes appox 16-18 lights a day. I have grow the same weed 4 times and the first 2 times used 24 hour light the whole veggy state and the last 2 times used 18 hour light and I had about the same results. The only thing different was my electricity bill was lower.I see you are going to order some products on line and would wait until it gets home and then start over. Also get a good book on growing. It took me a couple of crops to get a good hand on growing. I,m still learning. So just stay the course and everything will be fine. The weed you grow yourself is the best weed in the world!! Peace