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Re: [APD] carbonate test

Scott wrote:

> I wish I had the scratch paper handy with my notes. I
> thought I heard Roger say that the acid test as he
> described it could falsly indicate no carbonates but was
> unlikely to falsely indicate carbonates.

Did I say that?  Regardless, it is true.  The acid will not fizz unless there 
are carbonates present, so you can't get a false positive from the test.  The 
test can fail to fizz on dolomite (a carbonate) so the test can produce false 
negatives.  That's why if the test appears to be negative it is usually 
advisable to scratch the rock the way Bob describes it and test again on the 
scratched surface.  It's also advisable to test a rock at several different 

The test for dolomite is a little difficult.  There is also a dye test for 
dolomite but I doubt that many aquarists are going to that length to find 
dolomite.  Dolomite is soft enough to be scratched, so if you use the 
hardness test first then you may never get to the acid test.

Roger Miller 
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