I would just check it every few months, the issue is the pump is 3.5W, it is the equivalent of an old beetle, the motor is low HP and it doesn't take much of a hill to stop it. They also become less prone to this as they wear in. Calcium build up and bits of sediment and sand are the main things that cause this, but they are generally reliable as long as they are maintained, given the description of the set up, my guess would be some bit of regurgitated food is the cause.