The key to the whole process is 'Maintain'. You have to keep the FC at or above shock level to gain ground. Think of it as a war. Your troops are bleach, and when you're at shock level you have more troops than the enemy (algae). Each of your soldiers, however, are on a suicide mission: once they kill an enemy soldier, they can't kill any more. You need to keep adding troops to replace the dead ones. Frequent testing and dosing will make the process go as fast as possible, though there are too many variables to give an accurate time table.