Please Someone Help Us

[Whitz]

   We are urgently seeking help for my Betta (male) who is showing unusual deterioration on tail. Purchase back in April he was my very first fish, and I tried/have done everything to T with him.
He is in a cycled, 6 G Fluval Edge tank (alone), gets water changes performed each and every wk. faithfully, and water tested with API master kit, and is fed New Life Spectrum pellets.
He developed, literally overnight, a small "tear" just slightly inward from edge of tail. Then the "tear" continued to streak the color right off his tail in a streaky fashion, and progressing vertically between the rays, down towards the bottom of tail.
He had this same weird pattern of missing tissue/color streaking vertically down the anal fin, which also started to happen on the dorsal fin as well, and well, attached here is a picture of what he looked like after about a week or so (despite clean water and normal readings).
 
  As the deterioration between the rays continued down and upward, I feared whatever it was would gradually hit his body, and possibly end up being body rot, as the only pictures I'd found consistent with this kind of deteriorating was "pin hole rot" starting in middle of tail like his. I treated him with Kanaplex, as I read that it would be least damaging interNnally. He healed up actually, and the lines of empty tissue and color actually filled back in over the next two wks. and gained blue coloring back as well....until 3 wks. after the last dose. I now woke up to yet another area  that looked like a "tear" yet again, and it has since continued "streaky" patter of missing tissue between rays, and here we go again.
  Not sure what's going on with him, but I've gotten mixed answer from tail biting, to pinhole rot. If it is a rot, and (2) consecutive rounds of Kanaplex did in fact heal it up, should I be trying to use that again, or take another route at this point. Anybody seen anything like this before, or know what I'm dealing with? What do I do? I've spent hours, day after day looking online for help...to no avail. Please HELP my little guy. We don't know how to proceed at this point. I'm literally worrying myself day and night over this. Any advice would be appreciated.
 
 *First pic is the condition before Kanaplex
 *Last two are after Kanaplex, and shows two new "tear" like areas on mid upper right and lower bottom left "tear" like area 
   surrounded by a bit of darkening, and stripping the tissue and color right through the tail, and has since spread or "torn"
   even more since the pics were taken yesterday

 

[Mamashack]

Looks like an infection of some sort however I'm not familiar with the Kanaplex you mention so can't comment on that. 
What are your actual water test readings? Normal for one fish might not be normal for another so always handy to have the actual numbers and some fish are more sensitive to their surroundings than others. 
Keep the water clean and warm - betta ideal range is 26-30°C - not sure what the °F would be. Try adding some catappa products - either the actual leaves or catappa extract.
The extract will probably work quicker since it's already in liquid form and will start to work immediately. Catappa is Indian Almond Leaf and has excellent antibacterial properties. It is one of the types of leaves that they get in their native habitat which at times can be less than desirable when the droughts evaporate their surroundings, but it obviously keeps them in reasonable condition in the wild. Having said that most of the pet ones we get are aquarium reared so may not have their wild cousins' stamina.
A word of warning the leaves themselves can make the water look dark, altho the extract makes the water look less dark and more like weak tea. Personally I quite like it but everyone shares that view.

 

[Meeresstille]

It could very likely be he is tearing his fins on something and then an infection can take hold. Does he have any tank mates?
 
Test your decorations with a panty hose (nylons) if these get snagged, then so can your Betta's fins. Feel inside caves and things he swims through if there is anything sharp there. Do you have plastic plants in his tank? These are often too sharp as well, the better choice would be to add silk plants if you don't want to go with live plants.
 
Is your Betta's tank heated and what is the temperature of his water?

 

[Mamashack]

Of course I meant to say NOT everyone shares that view on my last comment.