Tomatoes are heavy feeders, and you probably should have put in some fertilizer when you planted them.
I used Mater Magic by Dynamite when I planted mine. It's a higher analysis and lasts longer than the Epsoma Tomato-tone. You put in a couple of capfuls per plant when you plant, and then a month later add 4 more capfuls. With the heavy rains, heat and humidity we get here, I strongly favor a coated, timed release product like this rather than faster-release fert. Much less fertilizer washed away into the storm water this way.
