FFOF is a difficult soil to start seeds in because it is pretty hot. Watering it every two days only made things worse.
Seedlings need very little nutrient for first couple weeks so it is safest to start them in a seedling soil. Yours may be able to grow through this but it will be stunted for a bit.
I sprout seeds on the weekly in custom soils that are way hotter than ffof with great results I trust it for my all of my breeding stock even if I only have a couple few seeds from a run they still go in that soil with out a second thought
your problem looks like light burn and or over watering
So a 21 watt led is to strong? How far should it be too be safe. I kept it close because i didnt want it to grow long and thin. I was trying for a shot and wide plant.
Soil to hot ? Too close light ? Nute strength to high ?
Mix more vermiculite into potting soil ( aerorated soils help heat escape )
Replace plastic with cut in half milk bottle or prop dome , plastic may be causing sharp refractions.
Check your osmosis levels
Half strength BAC root stimulator and great white shark , half strength important as it sounds like your soil is heavy water holder
Ive moved it into the tent with more light. But keeping the light further away. Also not watering it so much. She is thriving. I also cut off the 2 leaves that were burnt to death.