A friend who just sold his house with a pool gave me a bunch of something call Shock Plus 4 in 1 pool shock. The only active ingredient is Sodium Dichloro-S-Triazinetrione. Is that just a mixture of chlorine and stabilizer? If so I will use for chlorine and just keep careful track of my stabilizer level? Or is there something else in it that I don't want in pool. I know this forum recommends bleach only, but bleach is expensive and I would like to use this gift if it is safe.