Dying fish in stable aquarium

[VSingapore]

Your going to want to keep an eye on the ammonia when you cute back on water changes. If it spikes, you have no choice really. Definitely rehome some fish or better yet, upgrade to a bigger tank and get more fish

Sounds like a plan! Thank you for all advice!!

 

[VSingapore]

In freshwater the key to a good system is a a working symbiosis at first on a bacterial level
Then biological (sand dirt gravel rocks plants) mechanical ( filtration lighting ) chemical( food bottles dosed) for freshwater I like to do soil then sand then gravel for the media 2 in thick for finite cheating of organic inputs( more surface area = more bacterial growth/colonization then rock work... Most aquarium stores want us to do it backward and have filtration at the top... Yes movement and filtration at the top of the tank are important but a good substrate is sometimes overlooked in freshwater and thought to only be detrimental in salt. We can borrow many techniques from takashi amano of ada japan and the idea of a balanced system by using rule of 2/3rds 1/3rd substrate 1/3 rockwork and plants 1/ 3rd water.

Also here's a video from the fish sage

Father fish.

Interesting!! Thank you. This is exactly what I seek to learn and understand.

 

[MmeAssoc]

My temperature stands at 27-29C, I live in a country where I would need a chiller rather than a heater haha. (i.e. Singapore).

Indeed water flow is a bit of any issue for the Betta. I keep the flow at a minimum but without a sponge as im keen on getting water running through the system. Would a sponge significantly reduce the amount of water that circulates in the system?

Ha, well the water temp looks good!

I think the sponge does slow down circulation. Another option for your betta could be to heavily plant one corner of the tank with tall plants, which will slow down water flow in that area - will give him a spot to rest. However, he might be fine with the standard Fluval flow if his fins aren't too long. I noticed mine struggling to swim a bit once his fins grew out.

 

[Jay Hemdal]

There are probably multiple issues at work here. The female betta was likely killed by the male. The goldfish may well have brought some pathogen into the tank. In addition, there is a lot of fish for a five gallon aquarium, so as mentioned, you'll need to monitor the ammonia level. Fighting increases between fish in smaller tanks.

Jay