issue What's wrong with this ghost pepper?

[Calico Jack]

This image is of the ghost pepper I purchased from a nursery in June (the brand is chef Jeff), and then potted it in cactus soil. It was fertilized with miracle grow organic, before fruit set, and then fertilized with flower fuel 1-34-32, during the fruiting stage. Knowing that you can kill these guys with too much fertilzier, I did 1/2 strength early in the season, and only did full strength around July. The odd thing is, the Anaheim and purple ufo I started from seed, and then also potted in cactus soil (not an ideal soil, I learned the hard way) looks great and doesn't have yellow leaves. The top of the plant looks yellow, the bottom half is noticeably greener (immobile nutrient deficiency?) All three were in the same spot in my yard, and watered, fertilized at the same frequency. I see no insects, honeydew, or any sign of pests. They are in 3 gallon fabric pots. In zone 5B. May through August, we had excessive rains. Other than than that; typical weather this season.

Thank you for any insight you have!

 

[CaneDog]

These things aren't always easy to diagnose and cures can often be more general than specific. My thoughts are:
1. Provide more biomatter in the soil mix, e.g., some form of compost.
2. Changing to a flowering fertilizer is unnecessary at the least and likely counter productive, especially one so significantly skewed away from N. Stay with a balanced all-purpose/tomato fertilizer throughout the life-cycle as these are fruiting plants.
3. You might test whether your growing conditions are alkaline.
4. Different pepper varieties and even different plants within a variety will be affected differently by conditions. If one's doing poorly and others well, it doesn't necessarily tell you whether you're doing something wrong or have a bad plant. Here though, I think there are a couple tweaks you can make to provide more advantageous conditions.

Cheers!

 

[HellfireFarm]

As you observed, cactus soil is not an ideal medium. I would say it's probably not holding on to enough water - as CaneDog suggested, add some more organic materiel like compost to the soil.

As for different varieties, note that both the Purple UFO and Anaheims are annuums, while the ghost is chinense - even though they're both peppers they're different species. That's enough to have made the difference you're seeing IMO.