I know there has been discussions on this. And many people have stated that in a Vinyl pool you don't need any CH. What about for Propane Heater. Something about if there is not enough CH in the water, it can damage the metals?
You only need to maintain enough CH in the water to keep the pool from developing foam. Typically, water with a CH over 150ppm will be just fine for those purposes. Vinyl liners and heaters are much more susceptible from damaged caused by out of range pH values. The notion that your heater needs some level of CH in the water was an idea brought over form the water boiler industry where a closed-loop boiler requires some CH in order to deposit a thin layer of calcium scale inside the heat exchanger tubes to protect the metal. Pools are not closed water systems and the idea of scale protecting the metal inside the heat exchanger is really not applicable. Metal corrosion is entirely dominated by pH and so keeping your water properly balanced with respect to pH and TA is the most important thing.