Water level for sump refugium

[JoJosReef]

Sump plan is skimmerless with a cryptic and macro refugium in the middle between filtration and return. So far, added water to leak test and then added ~2" substrate (sand and Fiji Mud) and a nice sized pair of dried rocks from Marshall Islands and Fiji that's been rejuvenating for a month.

The rock is a bit tall. I might gain an inch working it deeper into the substrate, but not too much.

As you can see, the water level without the return pump (the DT isn't filled with water/sand/rock yet) is quite high. I understand that when that pump turns on, it will drop the water level in the return chamber to some level and then the water level in the middle chamber will drop to approximately the height of the circled glass:

If that is correct, then I lose about 2 in of height in the middle chamber. Pity, because I want to grow macros in there on a reverse light schedule and feed them to the foxface.

Is my understanding of the water levels in the sump correct? Is there a way to keep the water level higher in the middle chamber? Note: I also don't know what happens when you turn the pump OFF for maintenance (i.e., what volume of water is going to drain into the sump--we don't want an overflow, of course).

Any additional insight is appreciated! Thanks!

 

[Subsea]

Before you commission the tank, test electrical power failure by unplugging pump to see the maximum level rise in the sump. In that manner you can determine the maximum level that you can safely operate sump.

What macro are you feeding your Foxface and why do you need a higher level to grow macro?

 

[Cichlid Dad]

Did you build or buy the sump

 

[JoJosReef]

Before you commission the tank, test electrical power failure by unplugging pump to see the maximum level rise in the sump. In that manner you can determine the maximum level that you can safely operate sump.

Agreed. This is one aspect I'd rather have a calculation for before testing. @tbrown published an article here on sump volumes that Ilyhave to read in more depth. Would prefer to find out by "ah, I still have X gallons of margin" rather than "Nope, that's too much!"

What macro are you feeding your Foxface and why do you need a higher level to grow macro?

I don't have the foxface yet, but I'm growing Caulerpa peltata, Halymenia durvillei, Short and long branch codium (probably not palatable), Gracilaria hayi (maybe not palatable), and I have the smallest of stems left of my Orange Galaxy (Halymenia stipitata?). Was planning to try again with Portieria, Laurencia and/or Euchema. Although likely with the peltata I won't have room for another macro in that small sump! Great to hear from you @Subsea !

 

[JoJosReef]

Did you build or buy the sump

Sump came with my new tank, but I added a 4" tall glass weir wall to keep the refugium substrate in place:

 

[tbrown]

Depending on flow rate through the sump, your level in the middle section will be just above the baffle, correct.

 

[Subsea]

You can calculate all you want. Do your unplug test no matter what calculation. Sometimes you find out things that you did not consider in your math equation. Like drilling a syphon breaker in return line from sump pump to prevent backflow from draining display tank down and overflowing sump.

PS: Take 5 minutes to perform power failure test. It could save you a lot of grief. As a Marine Engineer, I have done the math and it takes longer to set up the calculations than 5 minutes. In general, the ratio of the two surface areas determines the same ratio for “rise in sump level” to “fall in display level”. The devil is in the details.

 

[PotatoPig]

The water level you need depends on the area of your DT vs Sump and how far your return line is below the surface of the display tank.

As tanks are typically a lot bigger than the sump the back siphon when the pump is off gets magnified.

Do an actual test, but for a decent first estimate:

Return Depth x (Display Tank Length x Width) / (Sump Length x Width) = Absolute minimum depth you need.

Example:
Return depth = 2”
DT = 48x18”
Sump = 30x12”
Backfill from siphon = 2 x (48x18) / (30x12) = 4.8”

In this case if you don’t have minimum 5” spare between the sump water line (while tank is running) and the top of the sump you’ll get salt water all over your floor the first time you turn your pump off

Note that surface tension makes this a little worse because it means the return nozzle can siphon an extra 1/4 to 1/2” out of the DT before it cuts off, which depending on your DT vs Sump size can get magnified significantly.

Don’t trust check valves for this. A valve failure could easily cost you thousands of dollars depending on your floor type.

 

[Cichlid Dad]

Sump came with my new tank, but I added a 4" tall glass weir wall to keep the refugium substrate in place:

The baffle on the right of the refuge is what controls water level in the sump from the first refuge baffle to that last baffle leading to the return. Two things. Most people run their ATO in the return chamber and that chamber would be the only one that would drop water level. You can add hight to that last refuge baffle to increase water level in the sump keeping the return as the only place water level drops, but you have to take in account head space for a power outage or return pump failure.

 

[PotatoPig]

You can add hight to that last refuge baffle to increase water level in the sump keeping the return as the only place water level drops, but you have to take in account head space for a power outage or return pump failure.

You can run it slightly differently, albeit with tradeoffs.

The water level can be above the last baffle, just the last baffle is there as a failsafe to limit the return pump’s access to water in case of a drain failure.

The ATO sensor still goes in the return compartment, which means the water level in both the second two compartments will rise and fall simultaneously. For the ATO functionality all this means is it kicks in less frequently but doses more when it does. Provided the area of the last two compartments isn’t huge compared to the tank salinity will still remain within a narrow range.