Can someone help me what this burn or yellowing on the bottom most leaves indicate?

Pluck the ugly bottom leaves. Stay with your basic watering/nutes and see what happens. If getsbworse worry. If clears..prob will..gtg. if not then we seek another option. Good ph..some calmag..some silica blast and watchem. Not every leaf will be perfect. Maybe a bit N starved. 2-2-2 kinda off for me. I go about 10-2-2 till flower then flower fuel at 1-34-32

 

Yep Get rid of any leaves touching the soil

 

That burn is pretty typical in fox farm ocean forest. That soil runs hot. Looking at the pics it's for sure not starved for nitrogen. Imo it looks like a possible N toxicity. When using just straight ocean forest you have to be careful with ferts. I ran into continuous issues with it and switched to 50/50 happy frog and ocean forest.

 

I run my Ocean Forest with no nutes during Veg and plants were over 8ft tall
Did use nutes in flower though.

 

Does look like too much nitrogen I also run happy frog and ocean forest. The more you water until run off the quicker you'll run through the organic material. I'll always start in happy frog, not due to any issue with ocean forest. For me seedlings and young to middle stage vegging plants don't need all the nutrients contained in ocean forest. A seedling has everything it needs off of its seedling case to make it through the entire seedling stage that lasts about 2 weeks. Happy frog has good stuff in it bat guano and worm castings what happy frog has that ocean forest doesn't is mycorrhizae. For a young plant mycorrhizae can help root growth dramatically. Photos I'll start in pots smaller than solo cups, all happy frog. Around 3 weeks I'll transplant into 1 1/2 gallon pots 50/50 or 30/70 happy frog ocean forest. After about a month I'll transplant into 5 to 7 gallon pots all ocean forest. I wont top dress for another 4 to 6 weeks or until plants start getting light or show deficiency. So using that method I don't start feeding until around week 12 through 14 from seed

Same with autos except I skip the 1 1/2 and go straight to 5 gallons 30/70 hf/of.

Ocean first feeds 4 to 6 weeks or more by itself

 

Did the 50/50 work well? I’m doing my first grow and went that route just Added a fair amount of perlite to promote drainage and oxygen for the roots.

 

works great.