Answer:

If the chlorine gets used up that quickly, you likely have some significant demand in the water. This can come from the excess heat, fertilizer overspray or drainage, heavy bather load, leaves, pollen, etc. You may also want to have your phosphate and nitrate levels checked by your local pool store. To make sure that you can easily establish a chlorine level, take a small sample (a cup will do) and add a couple drops of chlorine to the sample. Then test the sample, if the chlorine lights up that is good and you know you can add chlorine to reach breakpoint. However, if you still show "0" in the sample cup after adding bleach, you know getting chlorine into your pool will be difficult and you may consider a partial drain and refill to get fresh water in the pool, which is much easier to treat.