Having reread the entire thread and saw the picture of the fertilizer you are using I will have to change my previous opinion.
On you latest posting you showed 4 pictures. The first two are the most disturbing. Tomato stems are not supposed to be yellow and they look to be very leggy with little foliage. The third picture looks like a fungus and the last picture shows two things, leaf miners and fertilizer burn on the tips of the leaves.
The white fungus first: You can get rid of it easily by using a tablespoon of hydrogen peroxide in a quart of water. Or you can use a tablespoon of baking soda in a quart of water. You can use Neem Oil or a copper based fungicide.. TAKE THE PLASTIC OFF OF YOU PLANT. Yes, heating the soil will kill the fungus but the temperature required to kill the fungus will also kill your plant. All you are doing is making an airless environment, an environment perfect for growing fungi.
Fertilizer: That is a foliar fertilizer. For use on foliage. Your tomatoes roots need food too and this is why I think the stems are yellow. 19-19-19 is way to strong for most gardening uses. It is why the leaf tips in picture 4 are all brown. It was sprayed with too strong a mixture. Get some regular fertilizer, organic if you can, but if not something like 12-6-8 or 10-6-12 or even 10-10-10. About the best you can get is composted chicken manure.
Leaf miners; A minor issue not to worry about and once you have them there is nothing you can do except remove the leaf. I just ignore them.
What I would do at this time is get some more plants and plant them, keeping the plants you have and trying to save them. Your main problem was the nutrition the plants were not getting. A well fed tomato plant is a healthy plant. Yours started off good but during the past couple of weeks went downhill.
