The last one also died

I hate heaters! Didn't even need one in the climate zone of my city, don't know why I bought one! Anyways will burry the fella tomorrow morning... He was struggling real hard, good in a way that he was taken out of his misery.. Lets see now already got a FlowerHorn tank and a community tank of Orandas, Black Ghost, Blue Goramis, etc. Will retire the piranha tank for some time..
Wanted to know if prolonged oxygen deprivation can cause serious damage in fish like difficulty breathing and loss of balance even after maintaining normal oxygen supply later?
-It doesn't seem to be swim bladder disease or any infection cause it took all the fish together at the same time in a matter of hours... Seems real efficient and high level bacteria so no..
-Water quality was not the issue cause I changed the water the night before and they were fine.. Had a look at them at 3am in the morning and they were swimming around.
-Leaves us with either electrocution or oxygen deprivation. The later makes more sense cause the Pleco in my Piranha Tank survived and is healthy since they are known to live in low oxygen levels and varied temperature range.
-Or its a Act of God..
Anyways.
Lesson learnt :
* Avoid cheap heaters and if you can then just avoid heaters!
If you are not sure or experimenting with them never leave the heater on for long periods without checking in at regular intervals.
-Check your electric equipment from time to time for loose connections and avoid cheap quality stuff like extension cables, multipins etc. especially for aquarium equipment. They are the part that can flip the balance real quick.
Unfortunately I had to learn the hard way hope people benefit from my fish and the mistakes I made.
This forum has always been helpful and supportive
And thank you to F1.Vet, has always been helpful.