As long as pH is above 7.0, don't worry. Otherwise, add 20 Mule Team Borax to raise it. I suspect you need to keep your pool solidly at 15ppm, and not let it drop to 10.

Your troll may sell 5 gallon carboys of 12.5% liquid chlorine. If you get one, you'll need to give him a deposit on the carboy, and buy a spigot for it while you are at it. This will allow you to add the equiv of 10 gallons of 6% bleach, and you bring the container back for an exchange.