Beautiful Crowntail!!
Here's another weird situation for you. I have a Betta (not a crowntail) named Flash who does not like my tap water... He prefers store bought spring water.
I can condition my tap water to get it as close to the tank water as possible, but after a couple of days, he starts to get fin rot. When I change it again using store bought water (and only one particular kind), he perks up again and the fin rot disappears. I know this is true cause I've experimented a few times using both just to see if this was the case, and everytime I did a water change with the tap water-finrot...
I have another Betta (a crowntail) who has no problem with my tap water.....
Go figure!!??