Unexpected volume

I am currently a dark brunette but a natural blonde and I am trying to go back to blonde without completely damaging my hair. I have been doing some research on how to lighten your hair with shampoo and stuff and a lot of what I found point to selsun blue dandruff shampoo so I went and bought some.

On a side note before I continue, I'd like to add that I have super thin, flat, straight hair and I have tried every volumizing shampoo, serum and spray out there and nothing seems to work for my hair.

Well continuing with the Selsun Blue, I haven't seen any lightening results yet but my hair is really dark. The thing I have found since using it is that my hair is so fluffy and has so much volume it's insane. I don't know if this shampoo is bad for your hair if you don't have dandruff but I love it! So if you are looking for a volumizing shampoo and you are brave enough to try using dandruff shampoo, I highly recommend it.