The active ingredients are chlorides of sodium and potassium and clove oil, no listing for inactive ingredients. Directions: Add one tablet to each fish bag containing up to one U.S. gallon of water. Not for use on Food Fish and for fish bag use only.
If I remember correctly, I broke the tablet smaller for smaller amounts of water. I stopped using them and switched to adding oxygen to the bag instead because the fish buyers couldn't see the fish through the blue water.
I think your tablets may not be good anymore because mine are a nice baby blue color and in your pic they look grayish colored and not smooth textured. I don't know how you would be able to test your tablets to see if they were still viable.