04-07-2014, 11:38 AM
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Originally Posted by AquaJay
I would also have to agree with the poisoning. Ammonia was probably so built up under the gravel that the first time you used your vac you hit an ammonia pocket and killed the fish. That's why I personally use pool filter sand in my tanks.
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Sand can still trap ammonia and other nasty stuff under it. Dissolved organic compounds and other non-dissolved things can get pushed under it especially if you have cories or other fish that will kick up the sand. Gravel at least you can siphon all the way to the bottom and you don't have to re-do. Sand tanks it's a good idea to re-do them around a years time depending on your situation of course, sometimes you can wait longer while others it needs to changed sooner.
I'm not advocating for one or the other, just simply stating that each have their ups and downs is all. Ammonia can get trapped anywhere, it's just always a good idea to not expose them to it so much at one time.
Also I believe the OP stated the fish died before the water changes, still, ammonia and other compounds are most likely the reason for the deaths.