The indoor tomatoes is growing leggy, found a YouTube video about using a DIY grow box to solve this issue.

When growing seedling, seedling mix perform better than normal soil. With seedling mix, probably don't need additional nutrient until it outgrow the seedling pot (or stop growing).

For seedlings, grow indoor will have better survival rate that outdoor (even shaded area might be hoter than indoor).

If indoor doesn't have enough sunlight for the seedlings, you might want to experiment with grow light.

For plant in a pot, buy potting mix. Black soil alone might be to dense, mix it with sand/perlite and coco peat.

For transplant soil, normal soil (including potting mix or 6/8/10 in 1) usually doesn't have enough nutrient. Probably need to add in compost or fertilizer/vermicast before planting.

After transplant, don't expose plant to direct sunlight for a few days.

I grow one stem in water and another in soil to do a comparison.

Both are put indoor next to a window.

Transplant another clove to soil.

Transplant one clove to PET bottle with water.

Water turned murky easily, and bubble appears. No sign of life.

It is melting. End of story.

I suspect it is Lettuce, but can't be sure.