Hi, Jim,

Yep, your understanding is correct.

However, there are two ways you can safely drain your pool.

1. Drain 50% and refill. If your CYA is still high, drain 50% and refill again. That should do it. You could do it again if you wanted but that'll probably get you in a range you like.

2. Find a plastic sheet wider and longer on both sides than the depth of your pool. Spread it across the pool and start filling into the top of the sheet while simultaneously draining from under the sheet. Theoretically, you could do almost a 100% drain safely.