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[aylad]

If you can type the ingredient list from the container, that might help Pooldoc identify it....

[waterbear]

It is made by Pool Time, which is Chemtura so it is the same company that makes AqauChem, Bioguard, Guardex, Sun, and Omni. (In other words mystery goo). Since it is added to the pool and then you have to shock and shock again in 24 hours and it has a very long name (probably Disodium salt of ethylenediaminetetraacetic acid,
dehydrate, which is the most common ingredient in these products that are not based on sodium bromide but are ammonia based) it sounds like an organic ammonia source to form monochloramine when you shock. IF you are testing for free chlorine you will have none but if you test for total chlorine or combined chlorine it should show.