Oh man, poor little beauty!

Are those shreds of tail in the water with him?
Ask your grandma if there was any ammonia or nitrites in the test AT ALL. Sometimes people go by the "safe" "unsafe" "warning" and "danger" levels, and there can be poor water even in safe or unsafe.
I would definately go with an anti-bacerial medication, like one of the maracyns. It would look a little different if it were a fungal infection. Use one medication at a time and don't add anything else except possibly a bit of aquarium salt. Freeze dried bloodworms rarely carry diseases, but sometimes live or frozen can.
Poor guy..he's one of my favorites on the forum. I hope he gets better soon