We are new to the forum and are very frustrated with the pool store at this point. Over the last three years, we have gotten into a severe issue with high chlorine demand and extremely high CYA levels. We were barely able to use the pool over the past two summers and have spent ridiculous amounts of money on chemicals to no avail. When we opened this year, we had purple residue on the walls of the pool and the under side of our winter cover. Based on prior recommendations, we drained the pool halfway. We dry vacuumed the purple residue from the pool walls with a shop vac and vacuumed out the purple debris in the pool to waste. We refilled with city water. After refilling, we are still getting CYA readings of around 100 ppm. Does that seem possible? And if so, does that mean we need to drain the pool halfway again before doing anything else? We are strongly considering switching to the BBB method this year.