Crowntail Betta losing coloring

[bengaly32]

This is Proteus, my CT and he's been losing color for about a week or so. The top 2 pictures are him now, the bottom is before he became ill. I noticed his fins we're looking scraggly so I removed the Tetra Whisper filter I had running on his side. The location of the color loss really concerns me because of what I've read about Columnaris and Graphite Disease. The color loss isn't gray, it's more of a lightening, nor is it fuzzy looking. He's still active and eating but he's not his normal "flare at everyone and everything" self. I've been a Betta Mom for about 8 months so I'm still learning. I've already done 2 treatments of Kanaplex. I'm hoping this is NOT either of the diseases I mentioned but I'm not sure because I've read that they kill fairly quickly. Any advice for treatment?

As for the important water/tank info:

Divided 10 gallon tank-tankmate is doing fine, showing no signs of illness but I removed him to a temporary 2.5 gallon until Proteus is better

Ammonia: .25
Nitrite: 0
Nitrate: 20
pH: 7.4
Temperature: 82 F

I do weekly water changes unless I see there's a problem then I do them more often. I generally remove about 25%-30%. Proteus is due for a change but I'm medicating so I'm not sure if I should do one (but most likely I will due to the Ammonia presence). I use Prime for a water conditioner, along with a sponge filter and heater.

[TMaier]

My Betta’s colors changed and faded. He also started laying around a lot and stopped flaring. At first I was concerned he was ill and tried a few treatments. Finally I had someone tell me he was just getting old. I know he was an adult when I bought him a year and a half ago.