Avoid excess watering, yellow leaves are a sure sign of the plant getting way too much water.

How big is the pot? Is is sitting on a saucer?

It' s about a 10 gallon pot. I gave it some epson salt and have been watering it less. No change. It just sits there. Three out of four cherry toms are doing about the same. While one in seemingly identical conditions is thriving. don't get it. Thanks all.

Epsom Salts? Not sure if you want to add that. I think its magnesium, which is a miior and isn't usually put into potted plants. Allow the plants to almost wilt a little before adding water, and even for that, add just enough to wet the soil and see it sink in a little. For tomatoes a good all purpose fertilizer might help. Epsom salts are sometimes added to pepper plants to give them greener leaves. If the tomato leaves are curling down at their edges, its a sure sign of excess watering.