RIP Mr Missy - very rapid decline

[robbyg]

After about 6 months of a pretty active and happy life, MrMissy died last night. His decline was rapid - yesterday afternoon we came home to find him discolored and lying on the bottom of the tank, breathing but clearly unhappy. We immediately transferred him to a 1/2 gal tank with conditioned water at 76F, 1/2 tsp aquarium salt and some Betta Fix. He came to the surface a few times but jut lay on the floor of the tank. He died in the night.

We hadn't made any changes recently - regularly testing and making minor adjustments to his 10 gal tank (see here). The last 6 weeks or so he'd spent hiding most of the time in a new silk plant that we'd got for him (not in that video).

It was bizarre how quickly he went from a healthy fish to a very pale, ill little fellow. Any idea what happened? His vitals are below:

Housing
What size is your tank? 10gal
What temperature is your tank? 78F
Does your tank have a filter? sponge filter
Does your tank have an air stone or other type of aeration? yes
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? aqueon betta pellets
How often do you feed your betta fish? 3 pellets twice or thrice daily

Maintenance
How often do you perform a water change? every 2-3 wks
What percentage of the water do you change when you perform a water change? 30%
What type of additives do you add to the water when you perform a water change? prime conditioner, aquarium salt

Water Parameters:
Have you tested your water? If so, what are the following parameters?

Ammonia: < 0.15 ppm consistently
Nitrite: not tested
Nitrate: not tested
pH: not tested
Hardness: not tested
Alkalinity: not tested

Symptoms and Treatment
How has your betta fish's appearance changed? color loss
How has your betta fish's behavior changed? lethargic, bottom of tank
When did you start noticing the symptoms? 6 hrs after last seen normal
Have you started treating your fish? If so, how? see above
Does your fish have any history of being ill? no
How old is your fish (approximately)? 1 yr

[aokashi]

it is probable that the fish died frim nitrate poisoning...when was your last water change?
next time, I recommend you purchase a nitrate test kit
Sorry for your loss :(

[LizzyP]

Do you add AQS all the time? Prolonged exposure to salt leads to kidney damage. And, am I reading correctly that your ammonia is greater than .15ppm at all times? That could be a factor, too. Sorry for your loss :/

[robbyg]

Do you add AQS all the time? Prolonged exposure to salt leads to kidney damage.

Not every time, probably once a month for the last 2 months. Maybe that was an issue

And, am I reading correctly that your ammonia is greater than .15ppm at all times?

No, the ammonia was always very low. From the previous reply I suppose that we should have been testing for nitrate too but as we were replacing quite a bit of water regularly, I had assumed that the ammonia derivative compounds would also be rinsed away. We should have tested.

We said goodbye to him this evening.

[aokashi]

aw D: goodbye fishie. may you swim happily under the rainbow bridge!