Mysterious kale illness.

I am still having issues with my poor kale-lings. Their lower leaves keep turning yellow and falling off. What is up with that? :(

I have read that it is probably a lack of nitrogen in the soil, but I just fertilized...I think tonight I am going to do a water change in the goldfish tank and use the nasty goldfish water to soak the kale and maybe the nitrate waste in the fish water will perk them up.

Barring that, I'm not really sure what to do...

The spinach is kicking butt and taking names, though. And I've about decided that leeks are more trouble than they're worth.