11-14-2009, 01:29 PM
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Given your water hardness I doubt the rock could of killed them.Unless a large amount of it was used, like using it as gravel. I have very similar ph and GH and have never had issues using clam shells, which actively bubble in vinegar. Most are a couple years old and are slowly dissolving. A few shells or calcium based rocks will not hurt a tank with a fairly neutral pH and medium-high buffering capabilities. If it did you would of seen a moderate pH increase in the tank.
Have you used any cleaners/chemicals near the tank? anything you think could of gotten in them?