Yes it is a Hayward. I am not sure of the volume of my pool. It is an 15x26 oval and 52" tall. It's just a little sand. I don't think it would even be a pound if all put together. After I vaccume should I backwash? I have not had any pressure increase since the install so I have still never backwashed the filter yet. I was told only to backwash when your pressure increases? Is that right? Thanks for all the help. I just never expected to see sand on the bottom.