Seedling tips turned slight yellow

You need to transplant to your medium your using. With them small cubes you find that after 5 days usually roots start popping out.

This is nothing to worry about, but you will need to transplant your seedlings ASAP if you want their development to continue. They have by now, no doubt, have roots escaping from the cubes and looking for nutrients and to build an anchor for the plant to come. Cheers, Organoman.