Do the Chlorine test strips only detect chlorine or do they also change the color in salt concentrations (NaCl)?

Sodium chloride salt is not an oxidizer and will not react with any of our chlorine strips.

However, if you are using salt in pools as a source of chlorine, and your question is, “Can I use chlorine test strips in a salt water pool?”, the answer is yes. In this instance, you must use a chlorine test strip with the correct range, such as the Residual Chlorine 0-5ppm or Low Level Chlorine 0-10ppm test strips.

Salt is used to introduce chlorine to the water (no reaction to strips) but the salt generator or electrolysis unit takes the salt water and converts it to hypochlorous acid and sodium hypochlorite.  It is the hypochlorius acid and hypochlorite ions that are commonly referred to as “available chlorine.”  Hypochlorous acid is a strong oxidizer and will react with any of the chlorine strips.