Need help figuring why yellowing/burnt tips

I'm in need of some help please? I'm in week 6 into veg with all fem Gelat.OG. The room stays at a consistent 78°F and 55-58% humidity. Co2 ppm is set at 1200. I use kingled 1500w led lights set 18"-24" away from the plants. I use FFOF soil and FF nutrients. The nutrients I use twice a week at 1/2 the recommended chart amount. Lights have been 24/7 since I started this grow. The room is sealed with plastic. Im going to try feed the FF nutrients just 1 time a week. Maybe I'm feeding to much? Genetics?

Any thoughts?

Too high ec levels in soil.
Hot soil and lotsa nutes
Thats my guess. I hate ff soils they are inconsistent and i find them to be hot. I stick with sunshine mix #4 promix bx or hp.

Check out photos of K deficiency, they lookclose to your photos - https://www.growweedeasy.com/cannabis-plant-problems/potassium-deficiency

Check out this visual guide, might help. Best I've come across.

Found this

So I noticed that the top leafs are the ONLY leafs showing yellowing with dark veins and burnt tips. The leafs underneath are beautiful green and healthy. Could it be the lights are too low? They have been at 18inch for a while. So I raised the height of my 3 1500watt LEDs to 24inch about plants.

I also been flushin with using water ph6.0 for 10 days. Yesterday I used foxfarm sledgehammer with my water. 1tsp per gallon.. Hopefully these 2 things will fix my issues. What do you guys think?

I can't go higher. 2x2x4 tent. Light is up as high as I can get it. Placed my hand under it. Not a heat issue .

I've been watering since January 2nd. I did alot of research to conclude that I have a Sulfer deficiency.
1-13-21 I put 2tsp of Foxfarm Boomerang per gal of water. And wow my plants are making a nice turn around. Hopefully next few days all Sulfer symptoms will be gone.