Diagnoses Please

Hello. Second grow ever, things were going ok then the leaves stated looking odd. Tips of all have begun to yellow, pics are of a Chocolope which has the worst looking leaves. I'm four and a half weeks into flowering. Feed about half strength nutes about every three days (GH Trio with Kool Bloom), using a Solarstorm 400 about 20" from tallest plant. Temps are around 80 at hottest & humidity is about 40%. Growing in coco coir. Would appreciate any help, thanks in advance!
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It looked like nute burn to me and was going to flush with ph'ed water first thing tomorrow but wanted a more experienced opinion.

Four and half weeks into flowering might mean they are finished. Getting close to harvest time. Please take pics in white light next time.