Organic seedling died and had fuzzy mold on it.

Yeah, get a plain old jiffy pellet and put a germinated seed in that. Use plain water for a week to 10 days then very very weak nutes (some worm castings and that bio fish mixed into water, let sit for a few hours and then strained off would be perfect but make sure its really weak) for another week after that. at any point when you see roots start to stick out from the pellet, ut the whole thing in your pot with that soil coco/perlite mix. It will work then. What happened this time, is you made a mix way too strong for that lil seed, and it was too wet so lots of nutes and too much water = mold, fungus and death. They dont need nutes for the first week. Also, in future, when u make up a soil mix, mix it up- put it in pot, water it a bit so its damp and leave it for a few weeks. Keep it slightly damp and let the microbes do their thing for a while. Id never use a soil mix that hadnt been aged for pref a month or so... I make up my soil mixes well in advance and let them break down a bit before using em. The more additives and organics I add, the longer I let sit before using.

So it looks like the seedling has bent over and then got infested with mold. I would use good seedling soil for the plant's germination and then transplant into coco. This is relatively low in pathogens, looser, and of good quality free from mold spores. I would initially completely avoid worm humus and fish mix, as these can further promote mold growth. Especially worm humus also contains "negative" pathogens and mold spores, for example from dead worms, which such a young plant can't handle yet. I also think that, especially with coco, the risk of overwatering the seedling is particularly high. (I would always water from the bottom) To further prevent mold, to be on the safe side, you can sterilize the soil in the oven. I personally consider the addition of mycorrhiza, Trichoderma, and rhizobacteria essential. These make the soil and your plant quickly more resilient =)