Well if you want my simi expert opinion I would think root-rot that led to a disease. My friend is growing hydro and had the same problem and I told him to put some Hydrogen Peroxide and its starting to clear up a little. If you do this just do like a table spoon and a teaspoon to a gallon...
since re watering them with just plain water do you think the ph rapidly changed. The nutes are good don't change unless you start to flower then change.
If it were me I would have a bigger setup with a small ac if I could. I wouldnt take no more lights out cfls dont put that much heat out. ummm I would also try to up the nutes because on one of the leaves it looks like it needs more nutes. I also think from the pictures you will need more light.
I had this same problem on two little buds near the bottom of the plant, the plant was bad ass I harvested it dried and cured it and every one I know said it smelled like mold, but I smoked it anyways.
Its kinda hard to see the middles section but cfls can get really close to the plant as my last grow of some rocklock were pretty close. Yours don't look that close a matter of fact the two out side lights could actually be closer and not hurt it. The plant to the right looks either a little...