What kind of tester?

You need a K2006 or an OTO kit to be able to read chlorine levels high enough to accomplish something useful with some types of algae.

And . . . as Mom told you , CYA levels are CRITICAL! It's not possible to answer your "what's next?" question without that information.

1. You need to get a local OTO kit, and test your pool chlorine with it.

2. You need a CYA reading, preferably with a HTH 6-way kit from Walmart, since you can't get a K2006 for 3 - 4 days at best.

3. You need to read these 2 pages:

http://pool9.net/cl-cya/
http://pool9.net/test/