Ouch, that sucks
Sorry to hear it and good luck with things.
And not that you have enough to worry about (and I don't think it's the cause of the fish deaths), but nitrates at 35ppm is definitely something you also want to look at. (It could just be the fish feeding.) You may want to look into sugar, or sugar/vodka/vinegar dosing as a temporary stop gap measure (be careful not to overdo it, the sudden reduction in nitrates can shock things - also if you dose too much sugar your tank will go cloudy with a bacterial bloom).