My first question is how often and how much are you watering? Is there significant runoff? If you're growing in something with compost its almost certainly a peat based soil although some companies use coco in with organic inputs.
Its very hard to overwater plants in fabric bags with well aerated medium. This is a definite sign of overwatering. But I also noticed you said your light was 200mm above the plants, at what brightness? 100% that close is blasting them. If you wanna keep the lights at that height thats fine, but if your at 100% turn it down to like 30-50% brightness. At this stage of growth autos should be getting around 400-600ppfd. I like to keep my light at least 1ft away from the canopy preferably 18inches (it gives optimal spread for most LED fixtures). That's when I run my light at a higher brightness. If you dont have anything to measure your light intensity photone or ppfd meter both are offered on android and IPhone. You need a diffuser for photone which is more accurate in my opinion. A strip of paper to cover your camera lens will work or they sell a diffuser that clips over it for relatively cheap.
As for the watering before you sew your seed, fully saturate the pot you plan on sewing your seeds into. Wait a few hours or so for that water to hydrate every bit of that bag and get a feel for the weight. After your plant has established and gone into full vegetative growth (about 2-3weeks or when the leaves touch the edge of the pot) you can water when its about half that saturated weight, but dont let your medium dry back too much. It causes nutrients to concentrate in your medium and can lead to burn. As seedlings just try to maintain a decently saturated level to avoid stunting. I mist daily and water about 1 cup 4-6 days around the edges of the pot in 5 gallon containers. Also one more thing when your seedlings first pop up and until vegetative stage starts they only need 200-300ppfd. Also in peat based soils with organic or synthetic inputs avoid runoff, it washes out beneficial bacteria and fertilizer. A little bit is fine but if its just pouring out the bottom its bad, around 10-20% is preferable in coco mediums to asure the concentration of nutrients is staying consistent but you can monitor that more easily by measure ec of runoff compared to inputs, you cannot accurately do that with peat.
Hope this helps sorry for the lengthy response I just wanted to mention a few things new growers tend to struggle with.
