Excel - COUNTIF Function

Happy Friday! I am trying to use the COUNTIF Function on a worksheet that tracks how much liquid chlorine is used at 3 different water wells each month, each well having 2 chlorine cylinders. I'm not sure if my brain is fried from reading/watching all kinds of videos for the past 3 hours and trying to follow their instructions, but any time I put in a formula, I get a pop-up saying I've entered too many arguments. Even if I enter individual cells and use only the 3 that it highlights for me (more than 3 does not highlight). I've attached a screen shot of the worksheet (Figure 1) and have highlighted the area I'm trying to figure out. As you can see, it will be for multiple dates, on multiple lines, going through to the end of the month, with the total chlorine (CL2) tallied up on the right hand side. Chlorine tanks are changed out quite often and each tank begins at 150, depleting down to 0. Figure 2 shows a screen shot of what I'm getting when trying to enter the formula. Am I misunderstanding how the formula works or am I using the wrong formula all together?

Figure 1

Figure 2