I am new to pools and need some help. I have just started working on my water chemistry getting ready for summer. I took a sample to the pool shop and had it tested. I know I need a good test kit just haven't invested yet. The pool shop told me that my CYA level was 0 which was virtually impossible because it was 70 at closing and there was no way for it to go anywhere. The shop told me that I must have a very high chlorine demand and wanted to do an overnight test to evaluate. After calling back this morning she told me that I would need 33lbs of shock to overcome the demand from what the test showed. My water is pretty much balanced on the ph scale and after reading on here I would love to start using bleach for my shocking process but I want to know if this information is accurate? Can anyone point me in the right direction before I do something crazy and really get everything messed up? Thanks in advance.