So about that gravity feed...

[loyalhero90]

So I remember reading that sumps/refugiums can only work through gravity filtration. So two tanks side by side would not be about to feed back into each even with powerful pumps. However, I saw this one tank

http://glassbox-design.com/2009/the-remarkable-pico-reef-of-marcello/

Notice the little pot behind the tank that serves as a kind of sump area? I think the tank is not active anymore but how could a person make such a connection without the gravity feed.

[bluelunar]

The sump is actually below.

 

"Marcello maintains this reef via a chiller, DIY skimmer, sump, refugium and DIY kalkwasser reactor all of which are below the tank in a cabinet."

[loyalhero90]

Ah well... that is why I ask before dreaming!

[khuzdul]

The sumps that I have seen use gravity to move water from one compartment to another, but the compartments are side by side. Putting the sump on the same level as a display tank would not change the function of the sump using gravity to move water from one compartment to another.

 

There are plenty of all in one tanks with sump / refugiums using overflow and a pump, where the sump / refugium is essentially "side by side" with the DT, as well as HOB sump / refugiums which is above the tank rather than below that use a pump and overflow.

 

TL/DR coming up:

 

How you get the water into the sump from the display tank can be done by two pumps, but then there is always the risk that one pump out-runs the other and then either rate sump will overflow and the DT runs dry, or the DT overflows and the sump runs dry. Or one pump can get clogged / blow and the same thing happens.

 

You can use a siphon instead of one of the pumps. A siphon can work fine for two tanks at the same level (side by side). It will keep the water surface level between the two tanks equal, but once the water levels are equal, the siphon pipe will probably drain out and an air bubble will break the siphon. You could design the siphon to be a truncated W to prevent the siphon from breaking though. Then the problem arises where with two tanks side by side, the water pressure differential in side by side tanks is very small when one tanks water level is only a little higher than the other. Because the pressure differential is small, the flow rate between tanks through the siphon to equalize water levels is very low. Then a powerful pump would out-run the siphon. You could run a low flow pump, but that would not make a very efficient sump. If you increase the water level differential between two side by side tanks more different by running the sump almost empty, though you increase the flow, you would only have a couple of inches of water in the sump which then also makes the sump very inefficient.

 

As with the in-tank sump/refugium systems and HOB systems, using a simple overflow combined with a pump would be better than a siphon (either from DT to sump or from sump to DT), but then you need to cut / drill walls and make sure that the overflow is water tight. It would probably be better to just by a bigger tank and put in a bulkhead to partition out a sump area like the AIO tanks.

 

I think that having the sump below the display tank is more because if well designed and sized right, it can be "foolproof" for flooding (barring leaks), and it is far more efficient, rather than because it is the only way it will ever work. I could be wrong...

[uscgbeachbum]

Water will always flow from top to bottom due to gravity. So if 2 tanks are connected through an in-wall bulkhead or hang on back overflow and you fill one tank, the other tank will also be filled. Your sump can be at any location or height in relation to your main tank (above, below, beside it). All you need is one pump (to pump water from one tank to the other) and an overflow to connect the two tanks.