Two plants with minor issues please help!!

I have two plants that I’m having slight problems with and have never encountered this before but this is just my second grow also. The first plant is a jack herring auto flower around 4 weeks old and the top leaves have yellow tips and the second plant is bubble gum auto and some of the leave are curling under but they both still look healthy. So question is how do I fix this and also should I give it plain water for a day or two to flush out some nutrients if that’s the issue or should I alternate nutes and water every other day? Pics to follow!!

You'll need to provide more information on your grow if you're looking for serious answers vs. guessing. You'll also need to provide pics under white light...not purple light.