Betta fish just died, what could've been the cause of death (info inside)?

[Jack TH]

Colin is completely right. How do you get skin infections? Bacteria that naturally live on your skin enter a wound. You didn't catch it from anyone, it just lives there. Same applies here. You don't have to catch a pathogen from another person to get an infection, in the same manner a fish doesn't have to catch a pathogen from another fish to get an infection.

How is everyone else doing? Any symptoms? Is your cory still lethargic, has it got worse or better?

 

[AWE]

The Cory was quite lethargic in the morning, hiding in decor but after a while he started again his daily routine, swimming and looking for food in the gravel. Sometimes he stops and rests on the bottom with only his eyes moving but more than half of the time he's active. Maybe he's also getting older and slower.
By the way, is there something which can be added to the water without affecting its quality, to prevent bacteria and other nasty creatures from spreading or at least to limit it to a minimum?

 

[Colin_T]

Your Cory could be stressing from the tank light being turned on.

In the morning open the curtains or turn the room lights on and wait 30 minutes or more before turning the tank light on. This lets the fish wake up slowly and not go from dark to bright light instantly.

In the evening turn the room light on, then turn the tank light off. Wait 30 minutes or more before turning the room light out. This lets the fish go from light to dim to dark over time and they will stress less.

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You can add driftwood and some dry plant leaves (Indian Almond leaves, Oak leaves, Maple leaves, etc) to the aquarium and they release tannins into the water that stain the water brown. Tannins will reduce bacteria and fungus in the water.

You can also buy Blackwater Extract from pet shops and that does the same thing.

Doing big regular water changes and gravel cleaning the substrate will help reduce bacterial infections, and keeping the filter clean helps too.

 

[TallPaul]

Tannins don't look that bad actually. I have a piece of bog wood that leaks tannins and turns the water a weak tea colour but with the lights on its hardly noticeable. I just say it's more authentic anyway

 

[Fishmama777]

Thanks for the answers! So, 0 ammonia, 0 nitrite, almost no nitrate (10 ppm or so) and pH around 8.
I clean the filter with tank water every 2 or maximum 3 weeks and when changing water I also siphon the gravel every time.
The Betta was not that old, not even 2 years I think...
I know the stocking is not the greatest but it was a surprise acquisition made by my daughter, she bought the fishes without saying anything while on holiday at her grandma's and we decided to keep them... Long story...
Now if it was a bacterial infection issue, what steps should be taken to ensure the rest of the fishes are safe?

Hi, i saw all the replies from everyone else ... but by looking at the picture i am pretty sure your betta had flukes & over time the parasite will kill the fish, cause the answer that the fish is two years old & that's why he died is obscured ... when i bring home a new betta, i always empty the cup into a bowl, slowly add some of the tank water he will be going into, i mix some methylene blue + aquarium salt, thats just to clean him a little .. i leave him in there for 30 minutes, then i poure out most the water & get more tank water, mix Prazipro & add that to the bowl ... another 30 minutes ... then i take the cup he came in & scoop him up with the bowl mixture ... put the cup in the tank & let him swim out ... i keep almost all the light off, and treat him for a month with Prazipro, aquarium salt, a few drops of melafix + pimafix, stressguard, Maracyn 2 (only a week) & Parasite remedy (treats velvet) ... i found all have parasites & have to be treated or evenually the parasites will kill them.