Should I be concerned? Pics included

First the details:

Soil Grow
Fox Farms Ocean Forest Soil
Fox Farms Big Bloom & Fox Farms Tiger Bloom for nutrients (following the labels for general feeding).
Cal-Mag (following the label at each watering).
Water is Tap Water left out for 24 hours to evaporate the chlorine, water has been tested multiple times to only have around 80ppm before adjusting ph up or down, or adding nutrients...not sure that means anything but had to test out my tds meter after accidentally buying it, meant to buy a ph meter.
I do adjust the water to a ph of 6 - 6.5 before adding the nutrients.
Watering/feeding twice a week, approximately a gallon per plant

I was having trouble keeping the temps under 85 in my grow tent but that has since been resolved for about a week now and I'm now getting steady temps in the mid to upper 70s.

For the most part the plant looks very healthy, but as you can see in the pictures below, there is something potentially "unhealthy" happening.

Helpful opinions and advice are appreciated!

Left a couple of details out, this plant is in a brand new 4x4 grow tent with only one other plant, they're under a 600 watt HPS (iPower ballast and bulb, with a cool tube +reflector).

In the picture below the plant on the right is the plant that the close up pictures in my original post are from.

heat stress and a bit of nute burn if i dont say myself..

With only 600w as long as your 16 18 in away and have a fan on the top it shouldent be heat from you lights . MY guess is slight nute burn . How long has this been going on?

I've only noticed it in the last 3-4 weeks, which is also about a week after I started adding nutes every other watering.

Heat was definitely a problem until about a week ago though, so it quite possibly could have been a factor as well.

I did do back to back feedings when first starting the nutes too (forgot about that - I didn't read the label close enough), first grow noobness!

Based on the couple of responses so far sounds like it's nothing major, I'll keep an eye on it and if it gets worse I'll scale back on the nutes a bit.

Wonder if I should do the cal-mag every other watering rather than every. I guess I could try it and see if the yellowing returns that I was seeing just before switching to 12/12.

Plants look pretty robust over all. Don't do anything drastic.

BTW, thanks for the quick responses, much appreciated!

Just flush with regular water man then when you see better results start adding nutes start like 25 percent strength then move up i have a schedule feed twice a week and flush one so no build up happens but you should be good.