THis is how I understand it, chlorine comes in 2 parts, stabalized chlorine and "fighting chlorine" If there i isn't enough of the "fighting" chlorine in the water to fight anything that is introduced to the water, you can get an algae bloom. The cya binds onto chlorine and stabalizes it - which is good, because there will be a level of chlorine always maintained in the water. This will keep it sanitized, but if something new comes in there is no "fighting" chlorine to battle it. That's how so many people get into trouble with their water - they have enough chlorine in the water according to the kit, but the chlorine is binded with the cya, therefore not leaving any "fighting" chlorine in the water. Ben came up with this chart to keep you with enough of the fighting chlorine in your water depending on how much cya is in the water. Hope this makes it more clear for you, so you can understand the importance of keeping up with the chart. If you keep your levels consistant, you shouldn't have to shock. Just bring your chlorine up slowly and if you start to see the water change color add more sequesterant and take your ph down to 7.2.