I use a FFOF / Light Warrior Mix BUT .........I believe the combination of 2 premium soils are what is the problem. Both can sustain a seedling individually but used together seems TOO HOT.
I use a 50/50 mixing FFOF/Light Warrior in lower bottom 1/3 of container. I add 1 tablespoon of Hapoy Frog Fruit and Flower fertilizer (5-8-4) . Best of all, Happy Frog Fruit & Flower Fertilizer is formulated with premium ingredients like bat guano, kelp meal, bone meal, feather meal and other beneficial microbes to help convert fertilizers into vital plant food. Which will be at base area of container. I just water and let her rip ! This works great for AUTOFLOWERS , but may need a little tweeking for longer run photo seeds like
( Sativas ) or extended veg cycles.
Then I add remaining container space with FFOF ONLY ( some extra perlite - between 20% more ).
Never had a seedling burn , I germ and place into this mix. Once plant starts getting bigger and root mass larger it will hit the lower ( super soil ) mix and can sustain a plant up to week 6 with this. At that time , I add some hydroplex for blooming to push flower building. ( especially if I have a multiple cola plant ). Otherwise it is optional.
Remember to keep things simple.