Why would you switch. Kick back man and let her grow. She bot gona become a big plant over night, wait afews and then give her some nutes and then when she starts to show flowering give her some flowering nutes. These things take time bro, be patient and let her grow. Keep it up 12/12 don't mess with her. Get 2 fans and keep them oscillating and wait bro. Get a hygo-thermometer and keep the temp between 75-85 f. And humidity around 65%. That's all you can do. But don't switch back to 18/6. PATIENCE PATIENCE PATIENCE!!!