Mini-sump idea


I may be counting my chickens before they hatch, but I think I'm about to acquire a number of 1-gallon tanks for free.

I've already got plans for a 10-gal shrimp colony, and I don't care to start a snail tank at the present time, so I'm thinking about how to use a 1-gal tank as a sort of mini-sump.

This is what I've come up with:

A. air pump drives the whole setup -- I have several pumps lying around anyway, so why not?
B. instead of having the sump under the tank and using an overflow, I'm thinking have it next to the tank and use a direct siphon to maintain an equal water level in both tanks.
C. is biomedia -- balls, scrubbies, or similar. As water exits the bottom of the siphon, it flows through the biomedia until it overflows a large PVC pipe (E) to the right.
D. is a 5-inch deep sand bed. The bottom layers of sand will grow anaerobic denitrifying bacteria, reducing nitrates.
E. water will also flow into the large pipe from beneath after passing through the anaerobic layers.
F. one of the two airstones in the mini-sump is under the biomedia. It will flood the biomedia area with bubbles so that the aerobic nitrifying bacteria gets plenty of oxygen. Incidentally, any nitrogen gases working their way up from the deep sand bed will be off-gassed from the agitation (just like CO2 is lost from surface agitation).
G. the second airstone drives water through an airlift pipe up and back into the main tank.
H. is the outflow of the airlift pipe. I envision a simple waterfall trickling into the main tank.

So the idea is to get a slow flow of water through the biomedia and give lots of time for the highly-oxygenated bacteria to convert ammonia to nitrite and then to nitrate.

Meanwhile, an even slower flow of water is pushed down through the deep sand bed and denitrified in its anaerobic layer.

This is almost completely biological filtration; its weakness is the near-total lack of mechanical filtration. Lots of live plants and/or frequent gravel vacs would compensate. A small power filter would have to be used for adding carbon, which I only use to remove meds anyway.

It *should* (I think) be overflow-proof, as long as there's even a quart (or so) of space in the main tank (in case the siphon breaks) and as long as the mini-sump is sitting high enough that the water level is below its surface.

Any thoughts? Is this a horrible plan, or have I found a good use of some materials (PVC, air pump, and a hypothetical 1-gal tank) that I've got lying around anyway?


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I think your DIY is a great idea. It's similar to the $50 finnex refugium that is also 1 gallon.

But it's nice to DIY for different requirements.


Yeah, I like the Finnex design, and someday I might DIY something closer to that for a refugium. This sump would only cost me a bit of money for a few PVC elbows and some sand and biomedia... and if I got the HOB refugium I'd have to buy the sand and media anyway (to use it for this purpose).

Thanks for the words of support!

Matt B

It looks interesting, I especially like the idea of having the sand so anaerobic bacteria can consume nitrates. Best of all, like you said, you're only out a couple of dollars if it has some problem and the bio media can be used elsewhere.

Maybe on the inlet you could use a panty hose or something to try and keep it clean, that may restrict it too much though, I'm not sure. I'm thinking like a lot of extra material so it wouldn't clog up quickly.


let us know how it works out.

I'm going to be getting one of the finnex refugium soon. cheaper here if you don't want the light and a option to add a water pump instead of the air pump.


I hope your 1 gallon DIY fuge would be deep enough for a 5" DSB. The finnex fuge is already 5" in height leaving no room for creatures or plants.

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