So I used 2 of these...(one for high level, one for low)
they're in the return chamber in my sump.
Optical sensors are the go-to sensor if you want a reliability over a long period of time. The Neptune Optical Sensor plugs directly into the FMM allowing you to monitor the level of your sump, mixing station, or any other reservoir that has up to 1/4" thick walls. Includes Magnetic Mount...
www.bulkreefsupply.com
connected to this...
Neptune Systems FMM Fluid Monitoring Module Flow Monitoring Leak Detection Water Level Management DC24 Accessory Port The Neptune Systems FMM Fluid Monitoring Module offers practical solutions for real-world aquarium issues. Compatible with the Apex Aquarium Controller, it has four ports for...
www.bulkreefsupply.com
This is in my cabinet under the fish tank. Its plugged into the EB832. The Apex senses low level and turn it on. This little pump pulls water through like 40ft of tubing up from the basement. Been working flawlessly for a month. I also have another of those sensors at the top of the tank to check for overflows and a few leak sensors under the tank. I actually have 2 of these FMM's. So I can sleep at night.
This Product has been discontinued. This little diaphragm pump is an excellent choice for automatic top-off duty. Unlike other diaphragm pumps available, this little powerhouse can push water to 30psi. Please be aware this is not a silent pump, it does vibrate and makes a similar amount of noise...
www.avastmarine.com
Next you'll want to know the Apex programming. I have it working but don't want to share my hack job at apex programming. I want to get it to only run during certain windows and limit the runtime but haven't been able to figure any of it out yet. Going to need to set aside awhile to figure out all this programming.
Hope this helps, let me know what you wind up doing, I put a lot of thought into this method. Didnt wind up doing apex due to cost and bad stories about the pmup.