That seedling looks sick. You are already losing the battle. I hope you have more seeds. Put one in a Jiffy pellet, water with tap water, when you have a nice healthy seedling put it in your DWC system. You will find that most people here don't know how to figure ppm's and the newbs confuse the new newbs even more. That's why most have switched to EC. There is still math involved with EC too so I don't know if the numbers thrown around are accurate or not. If you get a some kind of TDS meter, read the instructions and learn how it works and keep your EC below .5 for small plants and gradually work it up to 1 EC if they can take it. Good luck.