Ok. I think that your light is a little too close and your EC might be a little too high. Move your light back - about 18 inches from the top of the plants. Little plants like that get heat stressed easily.A 600W bulb makes a lot of local heat. While it may be 23 degrees in the room, under the light it is much hotter. Try checking the temp right at the top of the plants and you will see what I mean. I also suggest running clean water in the system for 2-3 days and then resume feeding at .8-1 EC. When the plants get healthier you can bring the E.C. slowly back up. The plants do not need to be feed every hour - you were right to reduce the amount of times they are being fed - good job! They really only need about 3-4 feedings a day at that size. good luck!