Is this due to root rot? Temps? Or something else? Leaves have been curling down due a few weeks, and now they are starting to droop and dieback quickly over the last few days. There is some new growth still though. Do I need to uproot it and check / cut roots?
Yes, I do have fungus gnats! Thank you for helping me put it together.
Do you think there's a chance they have spread some fungus into the roots themselves and infected the plant already? I guess my first course of action is to deal with the gnats though. I'm thinking beneficial nematodes.
As far as I know they don't spread fungi, but the adults feed on it- they like moist soil for that reason. I have found short-term success with a combo of liberal use of Neem oil, sprinkling cinnamon in soil to control any fungus, and putting out water/soap/apple cider vinegar dishes near the affected plants (picked all the bis up from articles online). I don't know if this will translate into long-term control though!
I've had good luck with a product from Gardens Alive - I'm not sure if it was exactly this but was similar: https://www.gurneys.com/product/knock-out-gnats-trade-granules
As is typical for Gardens Alive, it's expensive; you maybe able to find something equivalent for less.
I’ve found that adding an inch of fine aquarium gravel on top of the soil and again in the drainage trays (enough to cover the drainage holes) eliminates gnats in a week or two.