You don't want to use that junk on tomatoes, especially in containers. You want a soil that is meant for outdoor containers OR raised beds. It should have a sandy consistency, and dry out easily between waterings every 2-3 days.

You also want a slow release fertilizer for tomatoes and vegetables plants. It's essentially processed and dried manure and other plants material that breaks up and feeds your tomatoes over 4-6 weeks at a time. During the summer you'll apply 2-3 times, and that will keep them pretty balanced on the nutrient front.

Looks to me the issue is the soil here here.

Bag soil tends to retain too much water. Has the soil been saturated for days?