What I see is a nitrogen (Nitrate) deficency.... worm castings,sea weed extract, alfala pellets or what ever MUST be acted upon by bacteria & change/break down the waste to nitrates so the plant can absorbe and use it. so there will be a delay before you see any change.

If you wish to use all natural you will also have to remember the plant can not use the nutrients until the microbes have had time for mineralization into a form useable by the plant. Al

Are they still in starter mix? If so, then add fertilizer! I use fish & seaweed myself. The plants will be able to absorb them almost immediately. Also, make sure you're not overwatering them. Yes, I know they need to stay moist, but I've always let them dry out a little bit before more watering. Also, make sure you are giving them plenty of light. Once the leaves emerge, I put mine on a sunny windowsill for at least half a day. Come transplant time, mine goes outside where they get sun from 1-6pm. Never a leaf burned, as they are use to the sunlight, unlike the ones you buy in a 6 pack, which are much weaker.

Good luck, and have faith. I find that seed grown impatiens are pretty tough.

I am really learning my lessons. You can not hold seedling hostage under light forever. For example Squash, Cucumber and Tomatoes. I had very healthy plants but after certain age they needed sun, they needed to go out. We know that plants make their own food by using carbon monoxide, air and sun. The ground still too cold to take them out and they started to fade. I know we all have the itch to start seedlings in February. You can for peppers and egg plant because they are very slow growers but for tomatoes, Cucumber and squash I will start the late part of April to take them out June first. Ground has to be 60 to 65 degree for the plants to grow.

foolishpleasure: photosynthesis requires carbon DIoxide, water, and light. ;-) It produces oxygen and glucose.

it looks like too much water to me..