Hot tub drained on its own? ok so last night i used an inground hot tub that have...

ok so last night i used an inground hot tub that have a PDA system ( hand held thing that turns everything on and off) any style the tub drained does anyone know how to refill it and how to keep this from taking place again? , by the way it is a salt wet pool and all that i turned on last hours of darkness where the lights and the spa heat
THICK LAYEr BOTTOM OF POOL:| please asnwer...
Answers:    I'm guessing this a pool and spa combo? If so, and it drained vastly quick after you turned on the spa, then you own a problem with the valve actuator on the return side. If it drained slowly next you may have a bad check spout on the spa by pass. To refill it a moment ago turn the system back to pool and run the filter and it will fill hindmost up. If it is a "spa only", no pool. you have a bigger problem. First refill beside a garden hose, then turn on the pump and look for leaks at the equipment. Let me know which of these scenario is closest to what happened and I will be able to assist you further.