1st knock your light schedule down to either 20/4 or 18/6. Your plant needs a rest period. 2nd get the temps up from 20c during the day. 24-26c if you can. 3rd let your soil dry a little in between watering. 4th make sure your water is correct range for your medium.
Cut down on the watering and get good air flow. Like the previous poster said get the lights on 18/6 cycle. That will give the plant time to recover during the 6 hrs of darkness. They also grow at night like us.