Heat stress or nute burn?

Hi, so I'm a first time grower but figure I probably spent hours and hours reading beginners guides, watching vids and getting all the important things into the brain prior to starting my little bitch.

I have a femenized Northern Lights under a 400w MH for veg stage, plan to change to HPS for flowering.

On day 34 (yesterday) I notice some slight tinged ends on some of the top leaves. I immediately put it down to being too close to the light and lowered it a good 25-30cm. I would estimate that at the time before being moved it may have been about 15" away from the bulb.

I don't think it is nute burn as I have only added a very diluted mix of charlie carp (an organic liquid fish fert made from european carp) with 9-2-6 and micro nutes. My medium is a premium grade potting mix so I figured it already has enough nutes for at least the first couple of months anyway. (Hence the very small adding of extra nutes)

I have always let it dry out well on top usually a good 2 days and then water well with tap water which has been sitting for at least 24hrs and is within the acceptable ph range for optimal growth.

Would just like some opinions on whether I should snip the burnt bits off with sterilized cutters or just leave them be. I've heard leaving dead stuff can lead to rot and or disease?

Cheers.