Betta Sickness?

[Tristan's 6000 Fish]

Have you tested your water?

Yes

If yes, what is your ammonia?

0

If yes, what is your nitrite?

0

If yes, what is your nitrate?

0

If I did not test my water...

...I recognize that I will likely be asked to do a test, and that water tests are critical for solving freshwater health problems.

Do you do water changes?

Yes

What percentage of water do you change?

21-30%

How frequently do you change your water?

Every two weeks

If I do not change my water...

...I recognize that I will likely be recommended to do a water change, and water changes are critical for preventing future freshwater health problems.

This morning I found my 5 year old Koi Half-moon King Betta unresponsive. His water is always clean, and he showed no signs of sickness, so what could've caused his unaliving?
I cleaned his water this past Friday, and he has been perfectly fine until this morning. He seemed happy last night and showeed no signs of stress., He ate at his normal feeding time, he wiggled at me every time I walked by. Kinda sad to see him dead. He was my most social and oldest betta, and looked very nice. There's no other fish in his tank, so no possible way he could've got diseases. I watch him carefully since I've had him, so if he did get sick I could treat it before it gets fatal.

 

[Jintoh50]

I realize this is an old post but I'm sorry for your loss. Recently lost my oscar of 7yrs and it sucks. I just started getting into betta's and, unless "king" is different 5yrs is a very long time for them, you must have taken very good care of him.

Here's my first betta, from cup to cube