Oxygen loss is also determined by the temperature of the water. The warmer the water the quicker it loses oxygen and thus harder to keep oxygen in the water when the pumps are turned off. I have my pond ran off 1 circuit and use an in-line light switch that I can flip to turn off the pumps when I need to do a little maintenance or sometimes I need to switch it when its very windy outside so I don't lose a lot of water from my fountain and spitter. My pond is only a 50 gal pond so oxygen loss would take quicker affect on the fish and I have already went 2 days with my pumps turned off and never had a problem. If you are worried about oxygen loss for the 1 day you have the pump turned off you can add some fresh water to the pond to give it some oxygen.

DavidAndKasie is correct. Heat pumps CAN be set back (turned down) effectively with a setback thermostat that has smart recovery. First, since you say that you don't understand much about how heat pumps work, let's cover that. A heat pump basically is the same as an ordinary airconditioner, with the addition of a reversing valve that changes its functioning to HEAT the indoors instead of cooling. Air conditioners don't so much MAKE cold as they MOVE heat from one place to another. In cooling mode, heat is moved from inside to outside. That's the hot air you feel blowing from the unit outside (the inside blows cool air). In heating mode, the unit picks up heat from outside and moves it IN (the outside unit blows COLD air, the inside WARM). There technically is heat in the air (or an object) down to scientific absolute zero (-459.67F) when molecular motion stops. It's cheaper from an electric energy expenditure point-of-view to MOVE heat than to CREATE heat. Thus heat pumps are cheaper to operate electrically than glowing-red heating elements. However, when the outdoor temperature drops, particularly to the point of ice/frosting, it's harder for the heat pump to pick up the heat and move it inside. So all heat pump system have an auxiliary heat source, typically standard electric heating elements, that activate as needed when it can't maintain the desired indoor temperature without help. This is called the "balance point" -- the point at which the heat pump can't move heat in fast enough from outside to counteract the heat loss that's occurring through doors, windows, walls, etc. Every system and house is different in that respect. The indoor temp drops below the setpoint (thermostat set on 70°F, room temp is 68°F for example), and a 2nd pair of contacts trigger in the thermostat which turns on the heating elements. Electronic thermostats may also do this based on time. If the system can't reach the setpoint (70°F) within a specific time period, or the thermostat senses that the indoor temperature isn't increasing or isn't increasing fast enough, the elements turn on. Of course, the heating elements pull a lot more electricity and aren't as efficient as the heat pump. So the trick after a setback (or having turned the system completely off) is to raise the temperature SLOWLY so the heating elements DON'T turn on. Electronic setback thermostats designed for heat pumps do this automatically. The computer figures out how soon to start the recovery process so it can raise the temp slowly and hit the target at the specified time without using the auxiliary elements (or minimizing use of them). It may take a few cycles for the computer to "learn" the characteristics of a particular system and get the timing right. You can also do it manually, but you have to PAY ATTENTION and not raise the temp too fast or too high at a time. This may take a couple hours at lower outdoor temps. Beware also that if the outdoor temp is well below the aforementioned "balance point" the system may NOT be able to recover the desired indoor temp at all without use of the auxiliary heating elements. Another aspect of heat pumps that you should know about is defrosting. As mentioned earlier, the outdoor unit in heating mode is basically cooling the outside. During some conditions, particularly wet/freezing weather, the coils can ice-up, like a food freezer that needs defrosting. Air can't blow through the coils when they're clogged with ice, so like a freezer they must be defrosted. The system does that by switching back to AIR CONDITIONING mode for a few mins so the outside coils get warm and melt the ice. Now remember that when running as an air conditioner, the system blows COLD air inside the house. During defrost, the auxiliary heating elements turn on, NOT for the purpose of melting the ice on the coils outside, but to warm up the cold air that would otherwise be blowing in the house. There's no way to prevent defrost from happening, the system does that automatically as needed. Some people say that if the outdoor temp is so low for an extended period that the system is running continuously, the outdoor unit is repeatedly icing over and defrosting, then it's best to set the thermostat to Emergency Heat, which shuts off the heat pump and runs ONLY the heating elements ... since they're being used a lot anyway during the frequent defrost cycles.

The pump motor is failing. It is drawing too much current and overheating causing the breaker to trip (either electrically or internally). You will require at minimum a new pump motor, and often a new replacement pump altogether is easier though a little more money. Since you should be shopping for a new pump you should strongly consider a variable speed pump. It will pay for itself over and over again in electrical savings. Here are some of the most popular models of variable speed pump and some more detailed info on how and why they save you money: Variable Speed Pool Pump Reviews

Not normal at all....you provide a nice anecdotal story with few facts...ie outside temperature, location, and system components...you should call installing dealer back out to take a look including checking refrigerant charge... While probably not related, do not cut system off..false economy and bad strategy with a conventional HP system... IMO