Pepper seed sprout issue

I read your post more carefully- I mentioned the temperature issue because that had been a problem for me in the past when I was relying on sun to heat the medium and we had a long period of cloudy days after starting the seeds.

Now I think your problem is that your home made potting soil drains poorly. If they sprouted but then turned yellow as they grew it might be that you didn’t buffer the acidity- which you must do but I don’t see how acid would stop seeds from sprouting because they rely on their seed for nourishment until the emergence of “real” leaves.

I think it is the seeds and low temperature. I started my pepper seeds in undrained flat trays with peat moss mixed with little perlite. I put about 75F heat mat under the trays. It worked very well. My old pepper seeds do not sprout. And the tray without heat has very slow and bad germination, with the same seeds. Pepper seeds need moisture and warm temperature. After seeds come up, i quickly move them to bigger cell trays with drainage, without heat.