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Tetra hardness test kit gone bad?

After the brief discussion of water changes, I decided to test both
my tank water and my tap water.  By way of reminder, my tank
water is still mostly soft Berkeley tap water, while my current tap
water is seemingly very hard.  (As measured by the way the soap
feels, the scale left on wet glassware that is allowed to dry, etc.)

I managed to find my Tetra hardness test kit, which is probably a
little over 2 years old now.  First I tested the tank water, and got a
KH of 5 and a GH of 6.  Reasonable enough, considering my 
original Berkeley measured about KH 2, GH 2-, and I've done one
water change and some topping off since I moved.  But then I
tested my tap water, and again got a KH of 5 and a GH of 6.  I'm
now very suspicious of the test kit.

I don't know how the GH test kit works (EDTA?), but the KH test
is just bromothymol blue and a standard acid solution.  The
bromothymol blue obviously hasn't gone anywhere, since the 
color is exactly as expected.  And I'd be surprised if the acid 
solution has gotten *stronger* over time.  Is there some other way
that this kind of test could go bad?

Wright- I know you are in Fremont as well.  How does your tap
water test?

David Ozenne
Fremont, CA