Crowntail Tail Loss?

[KellyLM]

Hello guys, I'm hoping you can help me out here. I'm not sure if he's sick, stressed, or what. My crowntail has lost his tail. Otherwise he's perfectly fine and his behavior has not changed.
I've attached a before and after picture of Spike, here is an album of more pictures: http://www.bettafish.com/album.php?albumid=2530

Housing
What size is your tank? .9 Gallons
What temperature is your tank? 82F
Does your tank have a filter? No
Does your tank have an air stone or other type of aeration? No
Is your tank heated? Yes
What tank mates does your betta fish live with? None

Food
What type of food do you feed your betta fish? Top Fin Betta Bits
How often do you feed your betta fish? 1 Pellet a day

Maintenance
How often do you perform a water change? Every 4-5 days
What percentage of the water do you change when you perform a water change? 100%
What type of additives do you add to the water when you perform a water change? Water conditioner and Tetra Lifeguard (we have 6 office bettas and are on industrial water, we lost three due to fungal infections in the first month, since I started using the Lifeguard six months ago none have died)

Water Parameters:
Have you tested your water? Not yet.

Symptoms and Treatment
How has your betta fish's appearance changed? He is a crowntail and has lost most of his tail. It has just now started growing back a little from what I can tell.
How has your betta fish's behavior changed? It hasn't. He's still a happy, extremely active little guy.
When did you start noticing the symptoms? I was out of town for a couple of weeks and his water did not get changed (despite my coworkers saying they would), when I came back he looked like a little black body swimming in the water with no tail.
Have you started treating your fish? If so, how? I have been religious about changing his water and I threw away his tree in case he was rubbing up against it. I also bought BettaFix and have begun adding that to his water in small doses.
Does your fish have any history of being ill? No.
How old is your fish (approximately)? I bought him from PetsMart at the end of February this year (2011).

[betta lover1507]

he might be a fin nipper, which means he bites at his own tail am not sure

[BetterBetta]

If he's a fin biter or it's fin rot... treat him with AQ salt- 1 tsp per gallon, it helps heal physical wounds and will encourage new fin growth. Stress coat also helps, its a conditioner that adds to the fish's natural slime coating, promoting growth and it helps destress a fish. Either way, put some decorations that are soft but colorful in his tank that he may be distracted with, incase he is a fin biter. He'll focus on the decorations more than his tail. Ping pong balls work fairly well for me.
Remove any decorations that can tear the delicate fins... You'd be shocked at just how fragile they are. Increase water changes to 100% daily if you can, clean water always helps-- besides, in something in about a gallon, water changes should be 100% everyday if not every other day to reduce ammonia and filth.

UPDATE: Stop bettafix, it harms the bettas labyrinth organ, creating problems in the long run!! Also, feed your betta two pellets two times a day, a high protein diet is healthy for them! Fast them once a week so they can digest!

[Myates]

Bettas should be in a tank no less then 1gal. At 1 gal you need to do 100% water changes at least every other day, some recommend every day. So you having less then a gal, every 4 days could be the reason why you have fin rot.
I saw the pic of your office mate's betta and I cringed. I'm sorry, but they should be in a 1gal+ tank each if at all possible.
With so few water changes your are building ammonia and other toxins rapidly in such a small tank, and it's becoming dirty quickly which causes fin rot.
It will catch up to them though, so please take it into consideration.

Is there any blackness to the edges of the fins? If not and he is biting himself it's due to stress.. they love to have hidey holes and feel secure so also may take that into consideration :)

[Myates]

Other then that, I do hope he gets better, he is such a handsome guy and I know you love him. Don't want to sound like I'm rude or mean, but it is something that is important for the well being of your fish. But keep us updated, good luck to you.