Chlorine is both a gas and liquid, not a powder. Sodium Hypochlorite is a liquid, not a powder. Calcium Hypochlorite is a powder but could be made into a liquid but cheaper to make and sell in powder form for
POOL CLEANING, not roof cleaning.
Re-read the label again, either you read it wrong or it is misleading.
There have been guys that have tried the pool chemicals that are powders before and it did not work.
If you would like to read about what they did, use the search button and search pool shock, calcium hypochlorite and powder roof cleaners and learn from their experience and experiments.
This has been discussed just about every year so don't expect a lot of responses, just use the search button.
The liquid chlorine or bleach is what most people use, not dry powders.