Eventually, the chlorine demand will go away but it takes time.

No way to know for sure but sometimes what happens to pools is that the CYA biodegrades over the winter and leaves behind a bunch of byproducts such as ammonia that cause a huge chlorine demand the following season when the pool is opened. I have a feeling that is what is happening in your pool.

The only way to get rid of the byproducts and thus the chlorine demand is to add lots of bleach. It will probably get a little expensive to buy all the bleach but there is no other way around it other than a lot of chlorine. Since you have no chlorine in there now, you must add some or you will not only have a pool with high chlorine demand, you will also have a green pool to go with it!

Each of the 121-oz jugs of bleach will add about 3.5ppm of chlorine. Go ahead and add 4 jugs this morning. A couple of hours later, test your chlorine and see what you show. You will have to use this chart to make a guess of what the reading is:> http://pool9.net/oto-chart/

This evening, test again and see where you are. And, then again, add enough bleach to get back up to around 15ish. It may take several days of keeping the chlorine high before the chlorine holds but eventually it will.

If you can get the K2006 kit, it will make this a whole lot easier.