Nutrient burn?

As soon as I saw the name "Happy Frog" I kinda knew what I was going to see. Happy Frog, just like Ocean Forest is heavily amended soil, especially with extra Nitrogen. These soils can be very hard to gauge as we don't really know what it's lacking or what it has an abundance of... So, ya, your thinking that it must have come from the soil, is my thinking too. Heavily amended soil, especially on seedlings, can cause havoc. I know this because I used Fox Farms Ocean Forest for my first grow and it was a constant battle. Firstly, I would continue to feed balanced distilled at 6.3-6.4 to even out the soil pH imbalance. That Nitrogen is probably locking out some essential nutrients that she's trying to pull, right now. I can only wish you luck that everything will be ok and that she will grow out of this condition. In future, and what I have moved to, is to use neutral soils. Non-amended soils that have all the good makings of a good media without the extra goodies thrown in. When you move from the solo's to a bigger pot, I suggest dropping the Happy Frog (I know you paid good money for it, but it may not be worth the hassle). When I did my final pot up in my first grow, from 3 to 5 gallon, I said screw the Ocean Forest and went for Dutch Treat potting soil to finish it off, and damn near all my problems went away. I still have a bag and a half of Ocean that I will not be using...ever again. Nutrient amended soils are attractive but in my personal opinion, just aren't worth the trouble when/if something goes sideways. Hope this helped my friend and happy trails. Good luck with the girl in the coming days and I hope all will be well. Cheers!😉👍