gordyjamz: I also have encountered the "yellow" calcium hardness test. I do not know why it is sometimes yellow initially rather than red. A comment on another thread suggested minerals, but that was not verified by any other poster in that thread. My tests for calcium hardness ran red initially but, except for one intermediate day, have been yellow since. I still use the test and count drops (x10) until the color turns a light green, rather than blue. Seems to work just fine that way. The results correlate with the results achieved with Ben's testing kit, which I've recently received.

Sandy