Two questions:

-- How do you feed your seedlings?

-- The potting mix looks a bit wet, but maybe you just watered. Do your containers have proper holes? I don't think the raised bed mix is the right choice for a small container, but I'm not familiar with this particular product.

Yellow leaves at the bottom of a tomato are often the result of nitrogen deficiency. I guess under- or over-watering as well.

I had only fed with a fish/kelp emulsion. And yes I had just watered.

how do I correct water deficiency?

I think it's probably natural. The first true leaves on my tomato seedlings usually turn yellow and die off. I don't see anything wrong with the rest of the plant. It even looks like you have a new seedling in the first pic.

The leaves on your other seedlings are not looking good though. Why are they so yellow ? Your containers do have drainage holes in the bottoms, right ?

Fish emulsion has plenty of nitrogen, so if you're giving enough, that is evidently not the problem. Just make sure that the soil is moist all the way down, and there is no puddling. Tomatoes don't like soggy feet. I think Epsoma is pretty sterile, so I'd suspect it's not a fungal problem, (although Epsoma does add a lot of "good" fungi, presumably after sterilization).

Agreed that since the recent parts of your tomato plant look fine, you really don't have much to worry about. The first true leaves on my tomatoes don't yellow and die though, but the cotyledon leaves certainly do.