I agree with Carl's post above with one exception --- I don't test cya every week. I always lose my cya over the winter and have to add some every spring. So, I test it upon opening, a week or two after adding the initial spring dose and then probably only one more time mid-summer. However, I use only bleach for chlorination. If you are going to use dichlor or trichlor, you'll need to monitor that cya level more frequently.