It makes no sense that these two items would not be included in HPI's main test kit. The fact that you have to buy them separately and then store them separately because they don't fit in the core set is very frustrating. It's also somewhat unclear how much yellow needs to change to count as a change. Also, there are no instructions listed on the bottle itself, so you'll need to keep a small piece of paper that says what colors you're looking for.
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