DIY Sump on an AIO tank having flow issues

[Petrichor]

I'm having issues with a DIY sump build on my AIO tank and I'm not sure if it's a non-fixable issue or just something that needs more time and patience.

As my tank is in a corner pictures of the back are hard to get, so I hope this MS Paint masterpiece is clear enough.

(not to scale, and unnecessary labels left out)

A Seapora Nano overflow box (blue) is in my main display tank (approx 24 gallons). It drains about 3 feet down to a 10 gallon sump with 1/2" and 3/4" tubing (red line). As I have a built in skimmer (gray text) for my AIO the sump will mainly be for live rock, heaters, etc. I have a Vivosun 800gph pump (green) as the return through 3/4" tubing and goes about 3 feet up into the tank. At the end of the return tubing is a u-shaped PVC tube. I have ball valves on each input/output tubing (yellow box).

Right now the return tubing is set to drain into the compartment of the main pump of my AIO (purple), which pumps fast enough to keep a constant waterline level in the display.


My issues are that I cannot for the life of me maintain a steady water level in the sump. I've fiddled with the ball valves repeatedly, but I can't get the water level to stay consistent. It's always rising or lowering, and it's usually about 1-2cm difference or more in half an hour. I think the best I got had about a centimeter of change in just under an hour, which is too much to last the night.

So what do I need to do? Keep fiddling with the ball valves? Less powerful return pump? New equipment? Is this even possible with an AIO tank that constantly pushes water into the main display? I am not mechanically minded at all and I've spent way too many hours failing at this now, so any and all help is greatly appreciated even if it's telling me I need to give up.

 

[Reef.]

Do you need two pumps? Does the pump in the aio serve any purpose?

 

[Brett S]

1/2 and 3/4 inch tubing won’t really be able to move a whole lot of water when it’s just being gravity fed. I suspect that your 800GPH return pump is just overwhelming the overflow. Are both drain lines running as a full siphon (where they are essentially underwater and there is no air at all moving through them?). I suspect you will need bigger drain’s or a smaller return pump or both.

 

[Petrichor]

Do you need two pumps? Does the pump in the aio serve any purpose?

The AIO pump moves the water from the back filtration area into the display. The tank has gravity fed intake to the skimmer, then over biological filtration, then to the return pump.

Thinking about it now, I could possibly connect the sump return pipe into the AIO pumps connection to the display tank, bypassing it completely. I'd have to look if that's even possible or within my abilities.

Are both drain lines running as a full siphon (where they are essentially underwater and there is no air at all moving through them?). I suspect you will need bigger drain’s or a smaller return pump or both.

Yes, full siphon on both. I bought the pump I have as it said it could do a max lift of 10 feet of head, which should be fine with the u-shape return. It's set on the minimum now, but maybe it's still too strong. I've had a heck of a time wrapping my head around pump lift height.

 

[Brett S]

The AIO pump moves the water from the back filtration area into the display. The tank has gravity fed intake to the skimmer, then over biological filtration, then to the return pump.

Thinking about it now, I could possibly connect the sump return pipe into the AIO pumps connection to the display tank, bypassing it completely. I'd have to look if that's even possible or within my abilities.


Yes, full siphon on both. I bought the pump I have as it said it could do a max lift of 10 feet of head, which should be fine with the u-shape return. It's set on the minimum now, but maybe it's still too strong. I've had a heck of a time wrapping my head around pump lift height.

You really can’t do a fully siphon on both. It’s impossible to tune the return pump to be able to exactly match a single drain (or two drains) in full siphon. Any tiny little change in flow will cause things to go out of balance and too much water will wind up in the tank or in the sump. Additionally, if anything happens to slightly impede the flow in the drain then you will have a flood.

The reason a bean animal or herbie setup works is because one drain is running at a full siphon and the other just has a trickle of water going through it. That trickle can vary slightly as the flow naturally changes slightly and keeps things working. Additionally the second drain will be able to handle the flow if the syphon drain gets impeded or blocked and it will prevent a flood.

To get this to work you need to only run one line at a full siphon and allow the other to just have a trickle of water running through it. To do this you will need to either significantly increase the size of the drain lines, significantly decrease the amount of flow from the return pump, or a combination of the two.

 

[Petrichor]

You really can’t do a fully siphon on both. It’s impossible to tune the return pump to be able to exactly match a single drain (or two drains) in full siphon. Any tiny little change in flow will cause things to go out of balance and too much water will wind up in the tank or in the sump. Additionally, if anything happens to slightly impede the flow in the drain then you will have a flood.

The reason a bean animal or herbie setup works is because one drain is running at a full siphon and the other just has a trickle of water going through it. That trickle can vary slightly as the flow naturally changes slightly and keeps things working. Additionally the second drain will be able to handle the flow if the syphon drain gets impeded or blocked and it will prevent a flood.

To get this to work you need to only run one line at a full siphon and allow the other to just have a trickle of water running through it. To do this you will need to either significantly increase the size of the drain lines, significantly decrease the amount of flow from the return pump, or a combination of the two.

I think I misunderstood what a full siphon is. I know overflow box runs off a siphon, and needs a full (no air bubbles at all?) siphon to work, but the tubing into the sump is not 100% filled with water. It drains to the ball valve and then there's maybe half the volume of water proceeding into the sump? Not a trickle, but defintely not full power. The return pump tubing is entirely full of water from start to end.

 

[Dom]

Interesting idea... adding a sump to an AIO. First time I'm reading about something like this.

Two pumps is going to make it difficult to balance flow.

If I were doing such a project, I would make the back compartment the entire overflow out of the display portion of the tank. Now you could put a tray with all of the mechanical filtration and still have a place to drop carbon and other media if necessary.

Then I'd install two bulkheads into the back compartment; one as a drain, which will flow into the sump and the other as a return.

The return might be a bit tricky as you have to plumb PVC from the inside portion of the bulkhead, back up and through the overflow and back into the tank.

 

[Brett S]

I think I misunderstood what a full siphon is. I know overflow box runs off a siphon, and needs a full (no air bubbles at all?) siphon to work, but the tubing into the sump is not 100% filled with water. It drains to the ball valve and then there's maybe half the volume of water proceeding into the sump? Not a trickle, but defintely not full power. The return pump tubing is entirely full of water from start to end.

Oh, ok. The overflow tube definitely needs to be a full siphon. Bad things happen if there is any air in that. It’s possible that your return pump is just exceeding the capacity of the overflow.

 

[Dom]

Oh, ok. The overflow tube definitely needs to be a full siphon. Bad things happen if there is any air in that. It’s possible that your return pump is just exceeding the capacity of the overflow.

There wouldn't be an overflow tube. The bulkhead would be installed at the bottom with a strainer. Only the return would have PVC which travels up and over the partition and into the display.

 

[Brett S]

There wouldn't be an overflow tube. The bulkhead would be installed at the bottom with a strainer. Only the return would have PVC which travels up and over the partition and into the display.

He said that he’s using a seapora nano overflox box, which is this:

That definitely has an overflow tube.

 

[Dom]

He said that he’s using a seapora nano overflox box, which is this:

That definitely has an overflow tube.

Yes. But I was suggesting a different approach, one that would eliminate the HOB overflow and the need for a second pump.

 

[Petrichor]

Figure I might as well update just in case anyone has similar issues in the future.

I ended up buying a 300gph pump off Amazon and 2 gate valves and what a difference! The smaller pump is more than powerful enough for my tank, and the gate valves allow way finer control than the ball valves, even though they were 4 times the price. I got it leveled in under an hour, and it's been going strong for 3 days now. Once I get equipment/rocks in the sump I'll be able to fine tune it even more.