Thank you Frank for the info and the welcome! Wow, I did not realize I was pushing the low temps that much. Great to know. All 3 in the tank were clustered right next to each other rather close to the glass, but the others (puffii and simplex) are much younger in addition to being different species— not sure how much that is relevant. I don’t have access to a scope but my husband has an opti-visor at work that I will ask to borrow. In the meantime I sprayed it thoroughly with the homemade Castile soap pest solution I use on my succulents and have moved all of them under some grow lights away from the window; at least the temperatures there are stable. In the worst case scenario, I have a warm snake tank that I place cuttings on top of for rooting (the heat lamp does wonders); maybe I could rig something up for the hydnos there.