Here is a closeup picture..

Newbie too, but all my reading points to needing to fertilize more regularly in pots. Give the tomato a consistent source of nutrients, as they wash out of the pot.

1/4 strength dose daily for 3 days, 4th day plain water is what I've seen recommended, and perked my potted tomatoes right up.

Have you read through the container gardening forum?

I'm not sure that the compost in the pots is helping. Might be compacting and keeping them from draining better. Definitely feeding them more often is called for when in containers.

Agree with Ed. You can't count on compost for nutrients in a container. There is no soil bacteria to convert it to nutrients. Container plants require weekly feeding. A common recommendation around here is 1/2 strength well-balanced fertilizer once a week minimum. More often if you are having to water daily.

Your watering regimen sounds a bit off too and is the most common cause of those yellow leaves. When you water do it well - until water runs out the bottom of the pot, Then do not water again until the soil 4" down is dry. Do NOT use the soil surface as a valid indication of the need for water. Stick your finger deep into the soil before watering. Keep in mind that over-watering kills more plants than under-watering.

Dave

This is just the nature of container planting, especially when it is down sized. It is not just about the tomatoes , it is universal. JMO.