Today i did a regular water change. All parameters were good, ammonia, nitrate, phosphate all 0, ph 7.2, and temp 80F. Replaced carbon. Everything was ok. I took a 2 hour nap, and when i woke my 12" arowana was floating head down on the bottom
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Does anyone have any ideas why he might have died? He had no injuries, was eating healthily, and wasn't acting odd.

. Does anyone have any ideas why he might have died? He had no injuries, was eating healthily, and wasn't acting odd.