This sounds very similar to my own water. I had a broken wrist and shoulder surgery over the winter and could only do water topoffs to tanks. Things were OK, then they were not with plant and fish die offs. With ApI test kit, water looked OK. Then got TDS meter. I got readings over 1000 ppm. Then used API hardness tests and readings were over the top. By then my right arm was better and I started doing water changes with distilled water and bought an RO system. Constant testing as it can be tricky to get TDS down without dropping kh buffer too far, too fast. I am finding that fish/ and most plants are Ok once I got below TDS of 800 ppm. Stem plants seem to hate this water the most. Anubias do not care. Crypts are OK but not as tolerant as Anubia.
I live in Northern WV, about and hour SW of Pittsburgh , PA. From my college Chem days, I know we do have high iron content and am wondering if this is a factor.