Bryan,

All the answers you need are he

http://www.advancedaquarist.com/issues/nov2002/chem.htm

Ben
Bryan wrote:
Just did some testing and got a problem. My water hardness has always been
on the low side of "normal" but not now.

pH is 8.4
Phosphates aren't registering
Calcium is at least 440
Ammonia, Nitrite and Natrate are perfect
I don't have a magnesium test kit but I add magnesium a couple of times a
week before calcium

The problem: my hardness is at 6 KH. I can't seem to increase that number.
My animals seem fine at night but who knows.

What can I add to directly pinpoint water hardness?

Thanks,
Bryan