You'll need to also add magnesium source if it's not the miracle grow for tomatoes. Also don't add any for the first 2-3 weeks depending on nutrients already in the soil, and add it at 1/4 to 1/2 of what the label says and work your way up or else you'll fry them.

But Bob's right, higher quality ferts will be better but if that's all you got, then that's what you're gonna have to use. If you can find pure blend pro series, earth juice, gh, foxfarm, advanced nutrients than go with one of those, but it'll be more expensive.