First of all, the ideal pH for hydro is between about 5.3 and 6.0. IMO, hydro does best when you let the pH drift a bit between those numbers. Here is a chart that shows the pH that different nutrients need to be uptaken by the plant:
http://www.marijuanapassion.com/forum/showthread.php?t=1908
How exactly are you checking your pH? If you have strips, I really do not believe they are accurate enough for hydro. You really need a decent pH meter. You should also be checking your ppms if you are not.
Your lights sound like 100w and 150 watt EQUIVALENT, not actual wattage. The equivalent wattage is a useless number when talking about growing. The 100W are probably actually 23-28W and the 150 is most likely a 42W. You have enough light for a vegging space that is 24" x 18" and a flowering space less than 18" x 15". Like Rosebud said, I also hate to be the bearer of bad news, but without more light you are still going to end up with a very very small amount of bud for your 4 months or so work. More better light is an absolute must.
While most plants do not show sex by 5 weeks, some do. However, your plant is extremely small for 5 weeks (we all believed that it was a lot younger) and is still not looking very happy. I know that you have invested 5 weeks in this plant, but especially if it is not good genetics, I think that you may want to start over. I generally have found that plants that get a hard start in life have a very hard time becoming big healthy. Find some good genetics and buy them. Do some reading on marijuana botany so that you understand the life cycle better. Read up more on hydro--your pH is off and I believe that most of the curling is due to that, not N toxicity. Your plants do show signs of nute burn though, so the nute solution is a bit high. Check out lighting needs (generally figured as lumens per sq ft), so you understand what size and type of lighting you need. You need a decent exhaust system set up and the plants should have an oscillating fan on them all the time. Unfortunately, this growing thing is kind of difficult. It takes a whole lot of time, knowledge, money, energy, dedication, and love--not like growing tomatoes or peppers.
