My best guess from the info you've given is that you are over-feeding a tad. Plants need very little to no nutrients in the first 3 weeks. The excess nitrogen could very well play a factor in the curled leaves.

You may want to look into some CalMag+ as well. filtering your water removes bad stuff but takes some of the micronutrients along with it. CalMag+ should replace those missing micronutes and return some color to the tips of your leaves.

Keep in mind this is based off relatively little information. I also may be jumping to conclusions by recommending CalMag+; it seems a lot of people (including myself) tend to do so.

Good luck. :thumbsup: