I'm with Matt on this. If you read 800 it would look like a snow flurry in your tank. How much kalk dosed? If your talking 4-5 tablespoons in the tunze that is hardly worth talking about, and you should be just fine. Oceanic is high in calcium, so I would take it easy on the kalk unless you get a bunch of stony corals or coralline growing like crazy. At any rate, I am sure you are OK if it is just the one fish you may just have a problem with that one. Let us know if you see anthying else that looks strange.