What's happening to my seedlings in RDWC

Thanks!! I did turn off the top feed shortly after posting this post and left the plastic covers off the top for a day and a half. The water level is about 1.5" below the bucket now. Things seem to be going pretty good so far.


Don’t leave cover off too long…

The ladies seem to be coming along pretty good but I’m seeing some brown spots forming on the older leaves. I’m suspecting that they’re not getting enough of something, thinking maybe calcium or magnesium?
I just changed the water yesterday and gave them some fresh nutrients so my ppm is now at about 430. PH always seems to creep up to 6.4 eventually. Currently at a 6.3. A little droopy this morning but they’re coming around.
Any suggestions on what’s causing these brown spots?