My betta died, I wonder why?

[purplecandle]

Hi, my betta died this morning and I can't figure out why. He seemed to be a perfectly healthy male betta except for one thing, I could not get him to eat. I tried all kinds of food and he only ate one half of a thawed blood worm. I never saw him poop either. I just thought that maybe he needed to settle in or maybe he was eating and I just did not see.

In the past few days he showed no signs of illness. Swam normally, active, interested in food (just would not eat it), made a few bubble nests, seemed to recognize me and so forth.

This really sucks. Last week I ordered a fish online and he arrived DOA..the past few days have just not been lucky for me.

Additional info.
10 gallon tank cycled for a long time
Filter had a baffle
Betta was acclimated before going into tank
I have well water
No tank mates
0, 0, <10 (api liquid tests). Tested before addition of betta, and after betta death.
Water change schedule - 50% weekly in addition to top offs and vacuuming of uneaten food
Do have a heater, approx 75°
No meds added to tank
Foods, tried everything, flake, pellet, thawed mysis, thawed blood worms. Also tried a feeding ring.

I also have the flu the past couple days and have not been cleaning so no chance that air freshener or spray cleaner got in the tank.

Is this common for a new betta not to eat? Was this a case of IPs? Did I miss something? Or did I just get unlucky?

[SnowySurface]

The only tip I can give is increase the temp of the tank. 75degrees is a bit cold for a betta since their preferred range is 78-80 + or - 2degrees. But I don't think 75 is low enough to cause death.

It seems like bad luck to me. Sorry for your loss.

[Picasso84]

I can't think of anything other than what SnowySurface said... I'm sorry for your loss :(

Was that your avatar? He was so pretty... I'm so sorry :(

[callistra]

Top offs that need more than once a week would lead me to think you don't have a lid.. it's possible that something was in the air and got into the tank.. anything sprayed.. even scented candles.. can cause this. Are you sure nobody else in the house might have lit or sprayed something?

Is this the first time you've kept fish? Are you sure your well water is ok for fish? Do you know the gh, and ph?