Yes peppers are fairly heavy feeders, apply some nitrogen. Also Don't let the peppers flower or produce fruit until they branch for the 3rd time. Pluck those flowers from the 1st crouch and the next 2nd set of crouches, otherwise the plant slows down it's growth to direct nutrients to the developing peppers.

Update, I fertilized and everything is fine now. New leaves deep green like normal. Some old leaves still a little yellow but overall it seems they needed fertilizer.

When you use only artificial fertilizers then you are dependent on the artificial fertilizers. Seems like some plants needed fertilizer to grow roots out of the potting soil. When the nutrients run out the soil is pretty lifeless. Looking at your pics it does seem you could benefit from a couple years of adding compost of some sort to the soil in a traditional way.

The way you spell "minnibells" makes me think of bells from Minnesota.

Of course, compost is a pretty weak fertilizer. The NPK is less than one. Also, it's not a "right now" fertilizer, but takes time to decompose to even get that small amount of fertilization out of it. That's why, with compost, the nutrients don't "run out". Except there isn't that much there to begin with. So if you have a right-now problem with nutrients, compost isn't the way to go. Compost is great for soil structure, but as a fertilizer, you need to load on large amounts to have any significant effect.

To the extent you need nitrogen, lawn fertilizer is a cheap and powerful way to go. My soil is naturally very rich in P and K, so I never need to worry about them. But nitrogen goes up and down, and leaches readily, so I sometimes throw on some ammonium this-or-that.

I did not claim that adding compost would add instant fertilizer, but I assume you knew that and are being sarcastic. I was just suggesting he could improve his soil in traditional ways since he claims to have multiples problems. Farmers have farmed for thousands of years without knowing their NPK averages.

You said "When you use only artificial fertilizers then you are dependent on the artificial fertilizers." Well, when you use only compost, then you are dependent on compost, and compost is a weak fertilizer that takes a long time to work. That was my only point. There are lots of good reasons to use compost. Fertilization, at least for primary nutrients, is not really one of them.

dan - Your statement "The NPK is less than one" is only relevant if you compared equal amounts of the fertilizers you are comparing. If you apply an inch of compost and an Inch thick layer of your favorite fertilizer out of the bag; then I agree the compost has less fertilizer value. However the amounts of compost that I suggested are not unusual; however I hope that no one is applying an inch thick layer of bagged fertilizer. You should know that the NPK values are based on weight. And lets not argue the weight of one is higher than the other.

That's very true. Per unit weight, compost is a poor fertilizer. But we use a LOT of it. Even then, it takes a long time for the nutrients to actually show up.

Good info guys thanks, learning a lot!