Curious...how often do you water? I just looked at a couple of the pix. (on a sloooow DSL conn.)
When I do a flush too close to the time I last watered, the soil stays too wet for too long, resulting in leaves that are yellow with brown spots. (like yours)

At least that's what I've thought had been causing it. Doesn't happen when I allow to dry-out a bit before the flush.

edit...how often do you flush?