Solid theory, but this is a new set-up with substrate that hasn't even been in an aquarium, much less go anaerobic. Perhaps that unknown "black sand" substrate leached something toxic into the waterIn a tank, I can't say for sure, but in the ponds in which I work, I'd say you flipped the body of water. Normally if you have a substrate that isn't turned over or otherwise aerated, anaerobic bacteria thrive in the substrate. When you pointed the power head at the sand, you stirred up this anaerobic bed and released hydrogen sulfide, which combined with a lack of a properly cycled filtration system, resulted in a dramatic DO2 drop, suffocating your fish (which is why they were all gasping at the top).
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My exact thoughts ..........Solid theory, but this is a new set-up with substrate that hasn't even been in an aquarium, much less go anaerobic. Perhaps that unknown "black sand" substrate leached something toxic into the water
I missed that somewhat significant (lol) fact somehow. That certainly changes things!Solid theory, but this is a new set-up with substrate that hasn't even been in an aquarium, much less go anaerobic. Perhaps that unknown "black sand" substrate leached something toxic into the water