Jerry Peck
We have some chemical engineers on this site, maybe they can answer the chemical mixture question.
If you are sure it might be frozen (that means there is very cold water in there), you might try pouring some very hot (not quite boiling) water slowly down the drain. As soon as it hits the frozen area (probably the tub’s trap as that is the only place which should be holding water), the very hot water will cool quickly, reducing any high temperature risk to the pipes.
Others may well shoot this idea down, but I don’t think you should be mixing all the other chemicals together.
