This is not a new pool, right? Do you have any idea what the CYA level was when you closed the pool last year?

Sometimes, CYA biodegrades over the winter and causes a huge chlorine demand upon opening in the spring. I'm kinda wondering if this could be what is going on with your pool. The only way to fix this is to keep hammering it with bleach until it eliminates the byproducts that are formed. So, keep adding bleach. It may take a lot of bleach but it will eventually hold. If you are home today, go ahead and hit it again. You really don't want to leave your pool all day today with no chlorine in it.