I have these cobra plants in northern Indiana I have 3 cobra plants that I received in the fall and put them in the refrigerator for 4 months so that they would be dormant for the winter.one was a runner that is growing great. I have the runner and the other 2 plants in seperate pots. The potting mix is 1 part peat and 2 parts perlite.They are all in the shade .
I hooked a water pump to a bucket that is insulated as I put 2 frozen bottles of water in the bucket at morning and afternoon. I have a small tube that splits 3 ways to water each pot the water from the pump stays around 60 to 70 degrees . The pump water runs over the surface of the pots for 2 minutes every hour.The timer runs this from 7:00 am to 10pm.The runners is green the other plant is 1 foot tall with green new growth doing well . The 3rd plant sentup a nice pitcher but then the old pitchers started to turn brown and the new growth has turned brown the 1st pitcher it sent up is still hanging in there but has darkened at the base of the traps tube. The water is ro/di water. Am I running the pump to much should I have the water tubes below the surface or is it alright for the crown of the plant to be submerged in water for 2 minutes( as the water drains very fast.
Your pump system is fine, you don't need to change a thing there. I also see you have the plants in white pots, and that's great too. I couldn't tell from the pictures, but avoid having the pots sit in water if they are currently. Here's where some changes might be needed.
Contrary to popular belief, Darlingtonia are not shade plants. They are going to need more sun than they are currently getting. Afternoon shade is a good thing in a hot Indiana summer, but they should have about 4-6 hours of sun in the morning. Try to rig something up so that the sun doesn't hit the sides of the pots, but the leaves are getting full sun in the morning. You should see some red in the fangs if the plants are getting adequate sun.
Let's discuss the plant that isn't doing well. Darlingtonia are subject to some root fungal diseases that contribute to their difficult cultivation. Warm temperatures and stagnant wet conditions favor growth of these fungi. This is why the cool root run, aeration, water movement all help keep this at bay if the plants are exposed to it. Sometimes even that, however, isn't enough. It's important to keep Darlingtonia pots up off the ground so they don't come in contact with regular soil which can harbor the fungi. (Cylindrocarpon and Pythium and been identified; Pythium is a common disease that attacks tomatoes and other Nightshades.) Keeping pots and tools sterile is also important. Watch your plant that seems to be having problems. For right now it would be good to get a bottle of Bayer 3 in 1 at a garden center and spray all the plants, and pour some of it into the soil of the worst affected plant. This product contains Tebuconazole which we've found effective in treating Darlingtonia if they are in early stages of disease. If you see green pitchers wilting, pull the plant out and destroy it. Once they get to that stage the roots are dead, and there's no recovery. If a crown dies, but pitchers are firm, give it time. They often send out new shoots from live rhizome.
For winter, see if you can find a place for the plants to be that doesn't involve uprooting and being put in the refrigerator. Darlingtonia are much more sensitive to repotting than Sarracenia. If you can find a spot such as a garage window for them to spend the winter, that would be better. In nature they are USDA zone 8; they regularly experience frost. Brief spells down to 20 are no big deal. Siskiyou mountain forms experience much colder conditions than that, but your plants are more likely coastal.
Here's a video we did a few years ago on Darlingtonia: https://www.youtube.com/watch?v=XebZMWy2SLU
Let me know how it goes.