Very necessary HOB overflow mod

[reggaedrummin]

my preference would be to run my tank drilled with built in overflows but I setup my aio long before I decided to add a sump and didn't even consider it. When it can time to plumb my sump, tearing down to drill just wasn't an option so I'm stuck with the dreaded HOB overflow.

They are notorious for causing floods and being noisy. Let me show you what I've come up with to solve these issues:

NOISE:
I removed the stock pipe and stacked progressively smaller pieces of floss in the overflow compartment. I also filled the tank side of the overflow with bio balls so it breaks up and distributes the flow of the incoming water. It's effectively silenced.

FLOOD POTENTIAL:
I drilled the side just offset from center of the water line and installed a bulkhead so that it sits mostly dry. The primary overflow is filtered with the floss and feeds my sump. The secondary overflow just trickles but is big enough to handle all the flow of my return pump so if the primary plugs or slows, the water level raises and the secondary handles it. The normal trickle of the secondary is great to feed a fuge or can just dump into the sump alongside the primary. Since I have a second overflow drain, I run a bigger return pump than I would have otherwise so my flow rate through the return is fairly high. The flow through the "u" clears any air that could get in it immediately. Also, the bio balls break up the incoming flow so I don't really get micro bubbles to begin with.

I remove and rinse the floss and bio balls once a week to prevent any detritus build up or nitrate production. I've been running this way for two years without any issues or "close calls". I'm just as confident in this setup as I've been in any drilled tank and really pleased with how quiet it is.

If you're running a HOB overflow consider modding it and you'll be glad you did!

 

[reggaedrummin]

Last pic didn't load...

 

[tzsetzse]

So you've plumbed a bulkhead on the side of the overflow box slightly offset of center. This drains directly into the sump/'fuge as it's situated just at the water line withing the overflow box. Siphon break with the main return pump still running drains the sump, pumping the additional volume into the display tank. So the tank itself could still possibly overflow or have i missed something?
If the power goes out BUT the siphon is NOT broken, then your mod will channel the siphoned water from the skimmer box until the tank level falls below the surface skimmer gate.
Neat idea but please explain about siphon break while main pump is still pushing water into the tank?
Thx!

 

[reggaedrummin]

I understand your concern, but I think you've misinterpreted the aim of this mod. Perhaps that's my fault for my choice of wording. Never-the-less, my primary concern was silencing the overflow and maximizing the volume through it in a way that wouldn't increase the likelihood of flooding. The only improvement over factory from a flood standpoint is the velocity of the water through the overflow and decreased micro bubbles forming in the overflow. I'm relying on the increased water volume through the overflow to pass air, decreased micro bubbles, and a bit of luck to prevent siphon break. It's the one existing flaw. It's a concern, but I plan to address it with a controller I'll be adding soon though I've lasted 3 years without siphon break so hopefully I can last another week or two...
I'll add that a HOB out of the box has two fail points, the first is the siphon, the second is the gravity feed into the sump. Mine now has a redundancy to remove one of the two. 50% improved