I’ve had my tank for a while, but within the past few weeks I’ve lost a few fish. 2 swordtail. They start to turn upside down & sink …till death. what can I do? I’ve done a water change already. My water condition is normal. I have one of the two swordtail about to die. He is separated in a different tank, sunk on the bottom, and can’t breath very well.
Most likely it is the water. The water contains chlorine that kills the fish.
You should apply water conditioner to your water. (Hypo)
And use Chlorine tester to check your water whether still contains Chlorine.