FWIW, I hear a lot of new growers using Fox Farms stuff that have problems with their plants, possible/probably from too high of nutrient levels. When the soil is too hot, it interferes with the water movement in/out of the roots and can cause the plant to look like it needs water...wilted. I use
Promix and don't have problems with overwatering...I don't thin it's possible as long as there are enough drain holes in the bottom. Your soil looks to be ok and doesn't seem water logged...I would cut back o feeding, especially if using Fox Farms soils. They seem to work better with well established plants. The reason I use
Promix, other than not having to worry about over-watering, is that there isn't any added nutrients, so I don't have to worry about burning delicate new plants. I also keep total control of my nutrients. I have found that I don't really need all that much to have a successful grow. I add some composted manure, wood ashes, and that's it other than 20-20-20 fertilizer about every 7-10 days. Its easy, safe, and dependable.
In summary, I think your plants look OK, but maybe the soil is a little hot. I wouldn't try to flush it out at this point and I would keep the plants going as they are. The bottom leaves often yellow...especially during flowering.