So, if this is a new pool and a fresh fill and you have put in only liquid chlorine, then there is no way you could have a cya (stabilizer) reading. That is why you are losing all your chlorine. It is expected that you will lose all your chlorine in a pool with no stabilizer. You do need to add some stabilizer, but just go slow with it. It takes about a week for all of it to dissolve. Aim for an initial reading of about 30. You can always add more if you need to but the only way to lower it is to do a partial drain.

One question, if you have only been using liquid chlorine, how did you ever get a cya reading of 40 in the first place?