A refrigerator icemaker needle valve can be used to refill water loss due to evaporation. It can be adjusted from a slow drip to a small stream. The small amount of chlorine dissipates quickly.
A secondary pump intake chamber like Charles suggested would be failsafe without altering anything inside the pond.
View attachment 69530 You could also install a float switch inside the chamber to save the pump.
Yep, exactly!
I think that would be the cheapest and best way to avoid these type of accidents that was experienced here. Also, I would make sure the secondary chamber is no bigger than it needs to be; otherwise, debris would accumulate in it.
Picture attached below describes how mine would be setup if it was only a low water prevention device. The pipe can be 1" or 3" or 8" or whatever. It is much like a sight indicator for water level except underground and with a pump or something else attached to the bottom.
Honestly, I would not rely on any type of switch for low water level prevention.
The sensors are really used so to not lose the pump. There are vertical float switches, most commonly seen in aquarium top off systems, except you are limited in configuration in a pond context when also involving a high level sensor; if you are only using a low level sensor, then they are great to save the pump. Major benefits of conductivity and vertical float switches is that they require much less space, that can easily fit in a 1" pipe acting like the secondary chamber outside of the pond. Bladder float valves, whether the bladder is a ball or bottle etc, require much more space.
Personally, I would only use water auto-fill devices for top-offs to replenish water that was evaporated or pond leak rather than using it to stop a pump or system from draining the pond. Auto-fill devices, such as bladder float valves, are designed to install on the water outtake so to add water rather than to stop water from being pumped out. Although, if the auto-fill device was installed on the pump/system intake, then it could be used to stop a pump from draining a pond?? I would be cautious to using the device like this since it was not designed for this.
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