Isn't superthrive a root stimulator. Anyways, I wouldn't give them any nutes for about 4 weeks. Probably burning them up. Do you have air flow? Looks wet in there. Could be root rot or stem rot.

They need to dry out in between waterings. Your 86.2 degrees in the pic leads me to think your average temps aren't as low as you say, considering you said you spiked at 85. Don't lie to yourself, fix it. I would say get a fan, exhaust, intake, let them dry out, no superthrive.

I think i may have read somewhere Jiffy isn't good for seedlings.