I went throught the exact same scenario 2 years ago. I opened with new water, shocked, couldn't get chlorine to register on my testing sticks. Neither could the pool store. They told me to keep shocking daily and eventually an FC would show up. I went through a 50# of dichlor in 2 weeks. I called BS. They called the manufacturer, blamed it on a "bad batch", gave me a replacement 50#s. They also through out the "chlorine block", so I did another drain and refill (with a vinyl liner, something else the advised me to do ). Started over.

Only added half the shock this time, got a very high FC reading on my sticks. Took a sample to the pool store, they did as well. Turned out they were using sticks to test as well, and I'll bet a donut the first sample bleached out the test strip from high chlorine.

Basically they made me nuke my liner and sold me way too many chemicals.

Thank God for this place.