# HOB with a Wet/Dry setup??



## HappyGrimgore (Dec 4, 2015)

I have an inclination to try and make my spare 55g tank into a wet/dry for my 90.

I have an older HOB filter that i had considered using as the way to get water out of the 90 and down to the 55. simply drill a hole in the bottom of the HOB (and seal it) so the water can flow down a tube to the wet/dry portion.. Put a valve in-line, and poof! its back to HOB functionality if i ever need it to be..

If the power goes out, both HOB pump and the return pump cease to work, making no chance of overflow possible..

Im sure its been done before??? seems too simple not to have been done already


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## smitty (May 7, 2004)

Not sure how a power outage would stop the HOB from feeding the sump below. I understand that the pump will shut off. But I think the gravity pull may still cause it to siphon from your tank.


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## jw85 (Dec 24, 2013)

I'm pretty confident that all your HOB would do is prime the siphon, and once started you wouldn't need the motor to run anymore.

I agree with the above poster - flood waiting to happen.

Never used one before, but do some research around some of the DIY PVC overflows, and after built share pictures online to get feedback to make sure the physics work. They are pretty easy to build and only cost a couple bucks.


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## alexau (May 17, 2016)

petros are big fish, one dies somehow gets in the overflow, i know its very very unlikely but it was just an extra hole and im 100 sure the tank won overflow.

the main idea is to put a valve at the bottom by the sump so i can adjust the water coming down, this way there will not be any water slushing noises.

same amount of water goes down and up giving very quiet setup.

i did something similar on a tank couple years back and it worked like a charm


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## Narwhal72 (Sep 26, 2006)

It's an interesting idea but I am not sure the physics of the situation would make it work.

An HOB inlet tube is not technically a siphon since the water level in the HOB is higher than the water level in the aquarium. You can't siphon from a lower water level to a higher one. HOB's work because the pump is pulling or pushing the water through the intake tube.

Now if your drain is lower than the aquarium water level it will work. You could drill a hole in the bottom of the filter and put a standpipe in to set your desired water level. This would still be a direct siphon and not a surface skim though. With direct siphons you run into an issue with water level differential.

As you increase water flow into the aquarium or reduce water flow through the siphon (say through a clogged inlet), the differential between the water level in the aquarium and the water level in the HOB will increase. This can often result in an overflowing aquarium. Aquariums use skimmer boxes as they can compensate for a change in differential within the overflow box weir while the aquarium water level stays constant.

Also keep in mind that the smallest drain you want to use is a 1" pipe or hose. Very few HOB filters are wide enough in any area on the bottom to accomodate a 1" bulkhead. I doubt even the largest Aquaclear could fit a 1" bulkhead. Although you might be able to use a MPT and FPT pipe fitting with an O ring for a smaller fitting. Drilling the brittle crystal styrene that Aquaclears use will be a challenge.

In any case the modifications would make future use of the HOB as an HOB impossible.

It would be imperative that the pump for the HOB only be used for priming the overflow. If you tried to pump the water out of the aquarium and then return it from the sump with another pump it will only end up in a flood. It is impossible to sync the flow between two pumps. Even a tiny variation will eventually lead to either the aquarium or the sump overflowing.
Andy


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## Handyjoe (Jan 11, 2015)

So you are using an HOB to pull the water up from your aquarium, instead of returning the water back to your tank, you opted to redirect it to your sump. It may work providing:
1. You are dealing with two motors (pumps). One for pulling up the water (HOB) and one for returning it from the sump to your tank (a return pump).
2. The two pumps have to work together simultaneously.
3. You need to balance the volume of the two pumps, i.e., Volume (HOB) = Vomue (return pump). Should you have a mismatch, you will likely have the return pump running dry and an empty sump and an overflow aquarium. It's because most of the return pump has more power (gph) than any HOB.
It's seems like too much trouble to deal with since the two are almost impossible to balance. Something get in the intake of the HOB and ....oops, you have a flooded tank.
I would advice against such setup.
Good luck!


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## SrsSarcasM (Jan 28, 2016)

To correct people above me, the HOB wouldn't act as a siphon because the HOB top is open to the atmosphere - you need a sealed system to generate a siphon (like just a pipe for water changes). If the HOB pump stops, the intake tube will not keep drawing water because the HOB water level is higher than your display tank water level. You can definitely siphon uphill, as long as the final output of your enclosed pipe is below the water level of your source.

Not what you want to hear but agree with all posters above.

We can't in good conscience recommend it because inevitably when something fails (either pump), there is a blockage, etc, you will end up with a flood. Check Valves should NOT be relied on either.

Balancing 2 pumps is basically impossible, it can work one day and then they can be out of sync the next due to changing water heights, accumulation on the pump impeller (affecting output), age, partial intake blockages, different water head to pump against, etc etc.

There are some products out there that have an external box that you hang on your aquarium and an upside-down U piece of pipe that you need to manually prime to start a siphon - this then drains to a sump. I also can't recommend these because they aren't self priming, if you lose power and the siphon stops and then power is returned, your sump will overflow your display.

If you want a sump, just drill your tank and install an overflow weir box of some kind. It really isn't that hard nor expensive. Go with a 3-pipe system like the Bean Animal.


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## Narwhal72 (Sep 26, 2006)

> To correct people above me, the HOB wouldn't act as a siphon because the HOB top is open to the atmosphere - you need a sealed system to generate a siphon (like just a pipe for water changes). If the HOB pump stops, the intake tube will not keep drawing water because the HOB water level is higher than your display tank water level. You can definitely siphon uphill, as long as the final output of your enclosed pipe is below the water level of your source.


You are almost correct. Once he drills the HOB to put the drain line into the sump there will no longer be any water level in the HOB unless he puts a standpipe in the HOB to create a minimum water level. That would still be several inches of water from the aquarium drained. Without a standpipe it will drain until the water level in the aquarium reaches the same point as the bottom of the HOB inlet tube inside the filter even if the pump is off.

Something I had not considered since he mentioned an older HOB and I just assumed an Aquaclear. If this were a newer design like an Aqueon where there is no siphon tube, then the only way it would work is if the pump is actively pumping the water into the outside chamber and then gravity draining down. However as others have pointed out, this is depending on a two pump system working EXACTLY in sync with each other which is impossible to achieve and will inevitably lead to either a flood or a run dry situation.

Andy


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## dledinger (Mar 20, 2013)

Narwhal72 said:


> You are almost correct.


Sometimes you sound more than a little condescending


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## Narwhal72 (Sep 26, 2006)

You are probably right. For that I apologize. Text conversations do not reflect the tone of how words are expressed well. I certainly did not mean it that way.

Without the drain pipe into the sump, what SrsSarcasm said was absolutely correct. The water level in the HOB would be equal to the water level in the tank and all siphoning would stop. But once you put the drain pipe in the HOB that was no longer true. Which is why I said he was almost correct. He missed that key detail of the setup.

Andy


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