You have to have a filter to build up the good bacteria. I do not know how an Angelfish has survived this long without one. The filter is the heart of any Aquarium. You need to immediately get your hands on a filter. Do you have anyone in your area with a established tank. You could use their filter cartridge or even a piece of it to establish some sort of balance. I would suggest you never do a 100% water change with an Angelfish. They are to sensitive to temp and water conditions. Good luck and keep trying. Doing to many things at once could be making the situation worse.
Read more: http://www.tropicalfishkeeping.com/tropical-fish-diseases/angel-fish-unwell-help-pls-researched-91235/page4/#ixzz1kij1uCvE
Indigo Betta's 6 gallon freshwater fish tank, Indigo SIP