Almost every inground swimming pool that has an inground spa share the same water. This means that they can also share the same equipment. But there is a drawback, the inground spa also uses the same water as the swimming pool. You can’t keep the water in the inground spa hot all the time and you usually switch the swimming pool over to spa mode when you want to use the spa. To add a chlorine generator to an inground spa sharing the water with a swimming pool requires a chlorine generator sized to the total volume which on average is 17,000 gallons. A portable spa is usually made out of fiberglass and is not necessarily that portable. There are a few makers of chlorine generators designed specifically for a portable spa.  The size of the chlorine generator for a portable spa will be much smaller than for a swimming pool and the power requirements will also be much less.