Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your situation, and wanted to help.
Again I do apologize that my colleagues could not aid you sooner. If you would still like assistance, can you tell me:
Since you noted Eco Mange worked, has he stopped losing hair?
If not, how long has Gizmo been losing hair?
Is he itching/scratching the area?
Any changes to the skin (ie pustules, pimples, redness, crusts/scaling, ulcers, or sores)?
Any diet change in the 2 months before this started?
What flea treatment did you use? When did you last apply it?
Can you take a photo of this? If you can do so, this will let me see what you are seeing. To post them online, you can use the paperclip icon on the tool bar above your text box. Or if you can't see that on your computer/phone, then you can post them on any other site (ie Flickr, Photobucket, imgur, etc) and paste the web link here for me to check.