Lower leaves yellowing, black spots, dark veins, getting worse

[wodawiatr]

Hi! Great forum. I have been searching high and low for a diagnosis for my tomato plants and I can't find anything conclusive.
I am growing cherry tomatoes in a pot on my balcony - they were started from seed and grew wonderfully fast. Over the past two to three weeks, the biggest leaves in full sun near the bottom have started yellowing. The problem is working its way up the plant and they are getting black spots, curling up, and have dark veins. Initially I wasn't worried because it was confined to the lower leaves only but now it is steadily working its way into the newer growth. I fertilise them with an organic fertiliser once a week or so and I am trying to be careful to not overwater them.
I have put some pictures of them here:



http://www.dropbox.com/gallery/63085...b/pom?h=beedce


Is there anything I can do? The tomatoes are growing but I'm concerned that the problem will worsen.


Thanks a lot!


Kolin