Sure. One gallon should increase your FC by about 4 ppm. You might check again later this evening though. Your comment about the "the water looks alright, a little cloudy" concerns me. I hope the FC was;'t too low for too long already. So this evening if the FC is down to 3 ppm, I'd add another gallon. Marty might even recommend you perform an Overnight Chlorine Loss Test.One gallon liq chlorine, 10%
Good job. As you put the chlorine in yesterday with 0 CYA in the water, it was going to be pretty much gone. So now follow the FC/CYA Chart, based on the 40 ppm CYA you added to the water. No need to test CYA for a week or so.
Target the upper range for that CYA for your FC each day. Which is 7 ppm FC. So when you test this evening, add enough liquid chlorine to get to 7 ppm from the level the water is when you test it.
Use a 10 ml water sample for your FC testing. One scoop of powder, Each drop of reagent equals 0,5 ppm FC.