Pepper Seedlings Turning Yellow

Over a week ago I noticed that dark patches were forming on some of the pepper seedlings leaves. The dark marks were only on the Buran variety. This is my first year growing Buran so I figured that it must just be the way the leaves of that variety look.

This morning I went down into the basement to check on the seedlings and noticed the leaves were starting to look pale and were yellowing. There are no signs of bugs or disease.

This is the way the seedlings looked on March 9th:

This is what they look like today:

You can really see the color difference if you look at the green leaves of the tomatoes to the right.

They look healthy except for the color.

This has never happened to my pepper seedlings before. I quick internet search said that the yellowing may be caused by:

-Over watering; which leaches the nutrients out of the soil

-Chlorine in the water

I did just water these, but they seemed to need it when I did. This morning I gave them a small amount of very diluted liquid kelp. The weather was nice today so I set them out in the sun hoping that would help.

I am guilty about watering them with chlorinated water. From now on I'll let the water sit out for several hours to evaporate the chlorine (I promise!)

I'm not sure what to do except to let them dry out and see what happens. Maybe I should start some back up peppers just in case? It's a shame if these don't pull through because they were doing so well. 

PEPPER UPDATES:
click here to see the status of the peppers on April 15th.
click here to see how the peppers were doing on May 1st.