Be careful with the product "Diamond Clear Mega Shock" by AMCO:
This product contains CYA! I found out the hard way thinking that I was using a bleach-only product. My CYA level crept up from 75 to 100 in four weeks by SLAMing for opening the pool and the maintaining FC. Here is an excerpt from the correspondence with the manufacturer:
"...Our product contains a small amount of Cyanuric Acid (stabilizer) but it's possible you might need some additional stabilizer if you notice the shock is being "eaten up" by the sun too quick. It's important to have good CYA levels to prevent just that..."
Back to 8.25% household bleach...