Lack of oxygen. Did you do a water change the evening before? Did the filter stop overnight
WARNING: Viewer Discretion Advised Video of Dead Discus is Disturbing!
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Not sure what happened in that video... going of Google Translation one of the comments points towards: ("Bio Gas from Substrate/sand")?
I believe the uploader is unaware/surprised to what happened to his Discus?
The Tank was over stocked and now 24 Dead
(Min £1K @£50 each Max Est: £2K to £3K costs in UK)
What happened?
Lack of oxygen. Did you do a water change the evening before? Did the filter stop overnight
Condolences to the owner, being safe always have an air stone/ pump generating oxygen.
Grasshopper
Francis
So sorry for your lost, more details can be helpful.
Cliff