I had some leftover test strips when I got my API master kit and when I tested the water with both the results were not even similar. I just threw them out. I have had the API kit forever, it never runs out. I think you can even replace individual tests if you run out of one kind but don't need the others. Some bottles last longer the others. For instance the low range
pH bottle only uses 3 drops per test.
I got mine at petsmart. Did you try to return them and they refused? If they did it may be because that's what they use themselves to test customer's water because it's quicker.