Preventing siphon pump overflows

[rogeragrimes]

So I ordered a CPR CS102 deluxe overflow (with Tom's Aqualifter pump) for my 120 gal tank to replace a manual siphon overflow I have now. Relying on a pump to maintain the siphon comes with additional tank overflow concerns, depending on if both pumps fail or if one or the other fails.

I have read a few ways to prevent the DT from overflowing onto the floor. Suggestions include:
"¢Make sure sump can handle additional water volume from either pump failures
"¢ Make sure that the overflow box is only a ½" to 1" below water level of tank (so that if siphon pump stays on but return pump doesn't, tank will only drain to siphon box level)
"¢ Make sure return pipe has 1-2 small siphon break holes ½" below water level to help break reverse siphon effect if both siphon and return pump fail
"¢ Make sure return pipe is only ½" to 1" below tank water level (to limit reverse siphon if both siphon and return pumps fail and siphon break holes get clogged)


The one failure I'm not sure if I have handled is if siphon pump fails, but return pump keeps going. Theoretically, the return pump could pull out all the water in it's chamber into the tank, which might overflow the tank and onto the floor. Some people have suggested putting an electrical float switch into the first sump chamber (or somewhere in the sump) to stop the return pump if the water level goes low. It seems that many/most of the float switches are unreliable and/or require additional relays and converters. Is there anything simpler?

 

[CStrickland]

I have a pump that is supposed to be ok to run dry. I've been using it a year and one time I lost siphon b/c of a stupid mistake. I had it hung on the side of the sump under a few inches of water so pumped about a gallon onto the floor and then just blew bubbles into the tank until I came home.
I'm sure it isn't good for the pump but the manufacturer says its not a problem. It's the eheim compact+ line

I worry about number two, if your box is only a little below the dt level the siphon might not flow fast enough to keep up with the pump. The bigger the difference between water levels the faster the water flows in a siphon.

 

[scubadan206]

I would avoid the CPR and the auqalifter at all costs. The small pump will fail at some point. Air will get into the syphon overflow and stop the overflow. It will first stop being powerfull enough to restart the syphon after a power loss, and then stop being powerfull enough to pull any air out. I am replacing my tank and building an external overflow just to avoid a HOB overflow.