Does anyone know what this is?

Lights: SF4000 at 20"
Week 4 flower
Humidity: 45%-50%
Temps:24°C-26°C
Medium: Canna Coco plus with perlite
So I was thinking it's probably PH fluctuations because I was using Calmag and it was messing with the PH of the water. Other thing was maybe nutrient burn because the plant does have some burnt tips. I've flushed the medium either way with plain 6.0 PH water, but i was just wondering if anyone could give me a bit of information. Thank you in advance.

Welcome to RIU

It doesn't look like nute burn to me. The color looks hungry for something. After you flushed, did you feed it with a corrected nutrient mix? Are you measuring ppm/ec on your feed mix? What nutes are you using, feed schedule?