Yellow lines on 2 leaves

Leave them alone. Just let them grow. In a natural environment, no one would be there to correct it.

If there's alot leaves with claw ends like the one pictured to much nitrogen. Can be caused by a lockout problem

Too much water and too much fertilizer for plants of that size. Let the soil dry well, then the next watering, go with clean water. No fertilizer. Follow up in the following days. Adjust the pH of the water to 6.5.

Google ph fluctuation in marijauna, compare the rust color and position of the colors and you'll see it's more then likely just that and a mild case

Definitely not light burn,

OO..100% that's the start of what could be a serious issue. Check out light heat stress. Either on Groweedesy or Royal Queen Seeds sites has nearly every thing you can thru real really. https://www.royalqueenseeds.com/us/blog-identifying-and-treating-common-cannabis-ailments-n90 There'll be a few. I'll try find the one I've of Growweedeasy. So many, Bid, check. I have the FC 3000.. funny now, I've never gotten light burn like that. I I was running much closer.. But come pheno/strains are dif. You gotta check these things out from the breeder. What conditions and so on it'll do best in. But, even at 100% at 45xm away. I've never got burns. Also your plants in week from the past few weeks. Are droopy these might be down to pure ventilation. As you are running an auto. Why don't you make it so so your light comes on for 15-9 and the 15 coldest hrs lights on and vice versa. Also if you are running on 240Volts the FC drivers lights can exceed 40-50cm so a fan blowing on the light from top of tent down will cool the light bars. Keep driver out of Ient. Try up ventilation of course and make sure you have a little sway your leafs at least every couple of secs. Good luck

maybe a little light damage? FCE3000 is a strong light. If you are running it 100% 18/6 cycle at a typical 18-20" height give or take, it's probably light burn. 24" should help but won't knock it down to 66% power. This light is made for a 12/12 schedule. An 18/6 requires 66% of that power. I'd set it at 65-70% and 18-20" away unless you used a light meter to choose 24" to maximize evenness of canopy coverage. 1/1.33^2 = 56% ... hmm that may be enough on its own. So, consider context not included here... any changes to light - power or distance? IF those blemishes don't worsen, i'd leave it be at current settings. if they just showed up, consider a little less power, another inch or two OR cut light cycle an hour or two. also, can be more certain i am right if the plants are very droppy last 1-2 hours or more of light cycle... if there is light damage occurring, this behaviour almost always coincides with it. Any recent changes to light can also take time to show effects.. a plant may be less impacted by 'too much light' the first day or two, but eventually will show similar behaviour.. just depends on how much over it is.