I don't mix my own, but use a commercial potting mix.
In the past, I have used commercial seed starting mix, but it is very expensive.
Sometimes I use just moist vermiculite for starting seeds.
I add vermiculite to the potting mix for starting alpine seeds.
I add peat to the potting mix for starting meconopsis seeds.
The potting mix probably gives some weeds, and some green algae, but sprinkling vermiculite over the potting soil helps. If molds show up, a spritz with peroxide water can help.
This is not really what you were asking, but no one was replying to your post.
