Death of my delhizi

Hi all. Looking for a little help on the death of my del. I have had him since he was a little squirt. Guessing 3-4 years. He has always been healthy and happy. He lived in a 210 with 2 big ornates. The 210 was looking a little crowded and the ornates are really getting big so I decided to put the del into my 135 with the Senegal and some dats. I do regular water changes and the temperature was the same. But almost a week after we moved him he died. Really at a loss for why he died. Both tanks healthy. Almost never lose a fish. Wondering why he died? Could the change of tank cause enough stress to cause his death? The dats didn't bother him. If there was something I could have done differently I want to learn for the future. Thanks.


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He's gone and I didn't take any pics. There were no obvious signs of trauma or illness. Guessing it has to do something with water chemistry? Although both tanks are healthy maybe the water parameters are different? Each tank accustomed to the water in its tank??? Idk. Just stumped.


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