Great question. It makes sense that there is over watering or not enough drainage. My seedlings were yellow when I got them but have recovered nicely now I’m caring for them (I am not a regular waterer!).

Needs some water

I’ve used seasol liquid in the past for fertilizing my veggie garden

Over or under watering can be the culprit. You may also have a nitrogen deficiency in the soil.

I think they can be over wet or to dry…

As suggested it could be a deficit such as magnesium, or nitrogen. Another possibility is mites. There are sprays available or you could use neem tree oil as an alternative.

There are many reasons why a tomato plant’s leaves turn yellow. Under-watering and over-watering can both cause yellowing leaves, as well as nitrogen deficiencies in the soil, a lack of sunlight on the bottom leaves, or a possible disease (which tomatoes have plenty of).

I would take them off and fertilise and you might check the soil as I think your over watering.

Needs more water I’ve found