You most likely have such a high chlorine level (and I don't see any amount - you could have added one teaspoon or ten pounds) that you are bleaching the color right off the strips.
Try this - take an 8oz tumbler out to the tub, and scoop about an ounce of tub water. Go to your kitchen tap and fill the glass the rest of the way up - about 8 ounces total.
Test THAT. If you get a healthy chlorine reading on this test water, then your tub is WAY over loaded with Chlorine.
HTH