I need a gas riser diagram for a pool heater
Can anyone help

We have no earthly idea what you have or how big the service should be. Your pool manual is the best source. If you don't have one, Google the manufacturer for info. Suggest you look at your hot water heater for guidance. As a general rule, black iron is run from the gas valve, a drop from a "T" is added with a nipple and cap for a dirt trap and a flare fitting is installed with copper line and shut off from the house gas supply, However, you may have a local code, be sure to check.