The two gallons is just to get some FC in the pool to slow the growth of the (potential) algae.
You can test if your pool has algae...we use this test. Link-->
Overnight Chlorine Loss Test
If you have visible algae, no need to do OCLT...time to SLAM.
To clear your pool, you will need to follow this process...Link-->
SLAM Process
Print it out, read it three times, keep it in your back pocket. Really helps to have a hard copy with you as questions pop up.
SLAM is a process we use to clear your pool of algae.
To perform the SLAM, you need a test kit that can measure high levels of FC. We also really need an accurate CYA test to know how much FC to add. The drop kit gives us that accuracy. ColorQ can only measure to FC of 10. SLAM level FC with CYA of 40 is 16.
The reason to believe? Link-->
How Clear is TFP Clear?