These strips are mainly used by brewers to check for chlorine in brewing water.  Free Chlorine and Total Chlorine levels can be detected with these strips.  Free chlorine will be chlorine in the water, typically added by a municipality. The Total Chlorine measurement will indicate the presence of chloramines (used by some municipalities in lieu of or together with chlorine).

Chorine is very reactive with organics. It will easily form chlorophenols (and others like chloroform) These compounds can be flavour active in beer at the ppb level. Think medicinal, TCP, hospital, band-aid, plastic smell. It will react with various husk phenolic components pretty instantaneously to form some of these pretty powerfully flavoured chemicals.

To remove chlorine, use sodium or potassium metabisulfite (campden tablets).