Ok well my profile may say I'm a rookie , but this isnt true ;) I have had a problem like this before and it's an EASY solution:
Get a CFL compact florescent light or any florescent(6500k if possible )and put it over your plant , keeping it as close to the ant as possible without burning it . Usually you can get pretty close (probably less than 2 inches ) to the plant . Do this for a week or two , after that I promise this will solve you problem because:
Your plant has put all it energy into stretching towards a light it cant reach . If you get that light close it will stop stretching at put focus in to other parts that will strengthen the stem . Also I would suggest low nuitrents for the next 2 weeks . I have brought ants BACK TO LIFE with this technique so it will work .
Keep it up . The first grow is the hardest but when it's done you will be HOOKED :)
The heat