Rich,

I assume the freshwater reading is correct. The Royale Phoenix system looks pretty simple. It has tubes placed in the tanks and remotely measures the pressure in the tubes. It's possible that the tubes are simply clogged. If so, it looks like you could blow them out. If blowing them out doesn't work, it's likely the sensor. If the fresh water one is working you could troubleshoot the others by connecting the gray or black tube to the fresh water sensor port and see if the freshwater sensor reads the level in the other tanks. I don't have the instructions, but I would guess you have to start with an empty tank after moving or disconnecting the hose to the sensors.

Good luck,