If you have purchased a 2018 season Intex spa, a built in pressure gauge is provided and will allow the spa tub to release air to the allowed air pressure. Please note that it will not adjust the spa tub wall by adding air, it will only release air when there is too much pressure.
For earlier models, inflate the spa tub wall until it is firm to the touch, then attach the pressure gauge to the air valve. The pressure gauge indicator should be in the green area for a properly inflated spa tub.
Please pay attention to air temperature variation! In cold weather the spa tub will lose some pressure due to air contracting. If this occurs, DO NOT add air since the air inside will expand again once the temperature RISES. You should check the air pressure in hot weather, and if the pressure gauge indicator is in the red area (indicating overpressure), let some air out to prevent the spa wall or inflatable cover air bladder from failing due to excess internal pressure.