Adding a HOB overflow? How risky is it?

[Mmonk005]

Adding a shoutout to Jeff at Lifereef also.

Comments:

1. The dual siphon is probably oversized. The biggest risk of a siphon break is too slow flow through a tube. Two siphons = half flow rate per tube for any given total flow. A single siphon version should be enough for a 75 gallon tank.

2. If you get the Lifereef version it’ll come with instructions to soft plumb with flexible PVC. Do. It’s cheap, fast and easy.

3. Get a DC pump with flow rate control.

4. Mitigate flood risk: Put the pump behind a bulkhead that limits how much water it can pump from the sump. Even if the siphon breaks this will prevent a flood as the pump flatly can’t access enough water for an overflow.

5. Mitigate Flood Risk Part 2: Set the water level in the sump so when you turn the pump off and it siphons water from the tank the sump won’t overflow before the return nozzle hits air.

6. Mitigate Flood Risk Part 3: Make sure the return nozzle is not too far below the surface. It will siphon until it breaks into the air. Don’t trust siphon break holes, make sure the nozzle head is set so it can siphon all the way without flooding the sump.

7. Mitigate Flood Risk Part 4. If possible put the sump in a plastic sheet (6mil thick) lined tub constructed using the stand base. This will provide an emergency overflow bath *

note: Parts 2-4 apply to any sump plumbing system, not just HOB.

I’m considering going with an HOB overflow and installing a sump, but I’ve been worried about the risks. You seem to have found ways to mitigate them, but I guess because I’ve never seen one with my own eyes and struggle to pick things up when I can’t put hands on them, I’m having trouble understand 4, 5, and 6. If anyone can help me better to understand, I’d appreciate it.

 

[TokenReefer]

I’m considering going with an HOB overflow and installing a sump, but I’ve been worried about the risks. You seem to have found ways to mitigate them, but I guess because I’ve never seen one with my own eyes and struggle to pick things up when I can’t put hands on them, I’m having trouble understand 4, 5, and 6. If anyone can help me better to understand, I’d appreciate it.

I ran a HOB over flow (eshoppes) for about 1.5 years without an issue, so much so that I stopped thinking about it at all. I stop my return when I feed and it would start the siphon back up like clockwork every time I fired the return up without fail. That said, I never bumped it and if I did, I'd have to adjust it and make sure it was good again (being cocked in any one direction affects the flow/siphon).

To mitigate risk I used a piggyback float (for basement sumps, etc) from home depot in the return chamber. If the water got too low (possibly indicating the water coming IN from the HOB stopped) it would stop the return pump from sending water up to the display so that it wouldn't overflow.

You also want to make sure that if the power goes out and your return cuts, you have enough left over volume in the sump for the water from the display to drain into (at the lowest point; usually the return). To mitigate this I simply kept the return nozzle right near the water surface so less drained down.

Ran a 40 with a 20 sump this way without fail for a while. Not so say it wouldn't have eventually but that's how I mitigated the risks...