Need some assistance with HOB siphon system.

[Aerimis]

Evening, all. I'm fairly new to the salt reef game here. Been doing fresh tanks for about 20 years, but just established a 130 gallon salt tank. Problem I ran into was that the tank I got is JUST a little too thick in the back for a HOB overflow system, so I constructed a HOB DIY siphon with a weir to run down into my sump. The siphon works great (about 900-1000gph), but the issue I'm running into is that in the event of a power outage, the return pump will shut down but the siphon will keep running and overflow the sump.

I'm open to any and all suggestions on what I can do to keep this from happening. Here to learn, after all. Thanks to everyone in advance for ideas/knowledge/suggestions.

 

[Quietman]

The best answer is during design. The sump should be big enough not to overflow the tank on a power failure (which you're very aware of according to the above) and/or not have the drain from tank too low to allow too much drainage.

If you can't raise the siphon point itself perhaps you can drill a siphon break hole. It's a small hole in the siphon that's below normal water level but above the point where you end up with wet floors. When water drains below the hole it'll allow air in breaking the siphon. Routine maintenance to keep that hole clean. Also I don't know where your return flow is but you may want a siphon break there too as water can reverse siphon through the pump.

 

[UncommonSense]

Are you using a water rated vacuum lift pump to maintain a continuous prime on your siphon?

If not, I recommend looking into the ubiquitous “aqualifter” pumps, and raising your siphon inlet up to be 1/2-1in underwater!

 

[UncommonSense]

Alternatively, the real solution is just biting the bullet and drilling the tank for an overflow!

—my first real overflow was just me with a hand drill and glass hole saw into my used 75g; a cheap 1/4” acrylic box made by the local plastic shop I cut some teeth into then matched my glass holes into; giving me a Herbie drain!