You sure are doing a lot of good work friend. Thanks for sharing your grow with us. Your leaves are cupping downwards because the roots are staying wet too long. I had the same thing happen to me when I used large containers. It may be a drainage problem with your bucket or soil but I'm not sure which. Anyway, you are doing a great job and thanks for sharing.
You may have too much soil in the container that lacks proper drainage. Make sure your have big drainage holes and put the bucket on mason jar lids to lift the bucket up in the drain trays for good drainage.