If your tomato plants have lots of fruit that isn't ripening, it may be that the plant doesn't have the energy to "feed" all of them. Imagine a mother cat trying to feed a litter of twenty-five kittens! If your plants are loaded with green tomatoes, consider removing some to let the rest get more of the mother plant's energy.

Tomatoes are a summer-time crop; the fruit needs warmth to ripen. If the ambient daytime temperature of the AeroGarden is under 70 degrees, you need to find a warmer place for it, or use a space heater (but avoid radiant heat!) to bring the temperature up. Not too warm - try to keep them under 78 degrees. 

You might also try a 'Rinse and Refill' and empty all the water from the bowl and refill with fresh water and fresh nutrients.  You can do this at every other feeding (once a month) to keep the nutrients balanced and give the plants a fresh water bath.