Phrag Fritz Somberg...Help ! Dead or Salvageable?

[Cearbhael]

My Phrag Fritz Schomberg got very sick. Was rotting from the growing tip out. I have 8 Phrags, 6 of them are Phrag Kovachii primary hybrids or Phrag Besseae primary hybrids. 2 are species...Phrag Peircie and Phrag Longifolium. I have them in specific Phragmipedium media in slotted pots with raised bottom to promote excellent drainage. I received them all in late March from Ecuagenera. Most handled the trip very well. Didn’t have trouble until summer when temps soared into the upper 90’s and stayed there. I live in Minnesota and it was a beastly hot summer. Fritz Schomberg was the first to show distress, rotting from the centre out. I treated it with Physan. Didn’t stop anything! The rest have been losing a leaf here or there from the outside. Always starting at the leaf tip. I have only 1 which has strolled through the heat with no issues at all, that being Phrag Ecuagenera Gigi. I have been keeping them in less than an inch of Distilled water. I give them dilute fertiliser and vitamin/minerals once a week and flush them with clear water once a week. Drainage cups are cleaned thoroughly once a week as well. The media has remained moist, I am sure sucking up water from the drainage cup. Should I be doing things differently? I normally keep Phals. Or Dendrobiums very successfully.
Back to Fritz Schomberg, I lost the last growth today, but... the rhizome and roots are healthy! I am very confused as to what to do! Can I get new growth from the rhizome or will it all rot eventually? What should I do differently in the culture? Should things be dryer? Should I rinse the media more often? Should I feed them more? I use distilled water with the food and vitamin/mineral concentrate. Diluted to about 1/4 the printed instructions. Should I keep the drain cup empty? ANY advice is welcome! I can handle criticism! It is the way we learn how NOT to do things