I don't think there is ever a way to ensure your overflow doesn't clog.  You just have to prepare for the worst in my opinion haha.

 

I think i'm just a little paranoid about possible disasters! haha, you could probably say i'm the king of fail safes.

 

I have quite a few other fail-safes on my system as well.  For instance:

 

I have strainers on both overflows to prevent a snail crawling down them.

I have a screen above my overflow box so nothing large than the teeth can get into the overflow box.

I have a leak detector that shuts off my return pump in the event of water on the floor. 

I wired a new outlet from my circuit breaker so that my tank is running on two different circuits - incase 1 trips it doesnt kill the power to everything.  The whole tank runs over 1000 watts so all of it being on one circuit seemed like an overload.

All the outlets used are GFIs

My controller has 16 controllable outlets that turn on and off 3 fans, lights, heaters, my ATO, return pump, 2 dosing pumps, and even the skimmer (if the temperature skyrockets, incase its the pump overheating, this happened to me once).

 

 

I tried to think of every possible thing that could go wrong and put a fix in place!

 

Either overflow cloging

both overflows clog

return pump clogs

power outage

single outlet(s) failing

circuit breaker trips

heater stuck on/off

ATO stuck on/off

Dosing pump stuck on/off

 

If you know of any other things that can break let me know and maybe I can come up with a solution!

 

If your overflows gets clogged and your ATO cant keep up with the dropping water level (prior to the controller shutting the ATO off) it will kill the return pump.  Normally this would only happen temporarily until the ATO catches up and opens the float switch again, but you can set your controller to do this:

 

 - once the float switch has shut down the return pump, don't turn it back on until I manually turn it back on.

 

This also prevents the ATO from ever malfunctioning and filling your whole tank with fresh water.

 

All this is probably overkill, but i like to think of every possible scenario and have a fail safe so I don't flood my house (and my neighbors, living in a condo above other people), not to mention kill all the fish.

 

The laser eye is the most accurate one available, and due to it hanging over the waters center its nearly impossible for a snail to get on it and block the eye, unlike a float switch, or float valve.

 

Just make sure the pump in the autotop off is located below the tubing output in your sump.  This prevents it from continuing to syphon after it turns off.

 

To prevent back syphon from the tank back to the topoff container, keep the tubing output high in the sump, so that its not underwater.

 

 

The only issue i've found so far is due to the design of my (and most) sumps.  How the baffles are set up, all evaporation that occurs is visible in the final section of the sump, where the return pump is located.  Because of this thats where your autotop off sensor has to be located.  The problem is, if one or both of your overflows get clogged, the level in the sump will go down - triggering the autotop off to refill the sump.  This would continue until your autotop off emptied itself, with your display tank overflowing.

 

To remedy this I have my controller set up to kill the power to the auto topoff if it runs for more than 15 seconds.  Solves everything :)

But you need a controller of course.