What are the dangers to watch for when cleaning a betta fish tank

I've had two fish who both repeatedly, if not all the time, go into my filter and stay there as if dead. Both did this, they're completely unrelated except for being bettas.

How I Set Up a Planted Betta Tank (Detailed Version)

How to keep your Betta fish safe when you are cleaning their tank or feeding them - Quora

What are the rules regarding Betta Fish fighting? Is it illegal in America? - Quora

Can you make your own fish tank gravel cleaning tool? - Quora

my betta tank has become very overpopulated with freshwater snails, though the algae in the tank seems to be withstanding their appetite. what should i do? is the algae dangerous? : r/AquaticSnails

Betta Fish Laying On Bottom Of Tank - All Reasons Explained

What are some good tank-cleaning species for a 5.5 freshwater Betta tank? - Quora

What are the risks of moving an aquarium with the water and fish inside of it while cleaning/moving it, even if temporarily empty (tanks are heavy)? - Quora

What are the risks of keeping a blue tang in an aquarium? - Quora