Reverse DSB /Cryptic Sump

[shall72769]

Inspired by Lasse (thanks Lasse for the advice!) I’m considering building a custom parallel sump where one side functions like a normal sump and the other half contains a cryptic fuge and a separate reverse DSB/chaeto pod fuge. Eventually the hope is this would be a skimmerless system.

Has anyone attempted this? I’m trying to build in as much natural filtration and diversity in my tank as possible. Looking for any ideas/advice on this type of build.

Hopefully once I figure out a plan for the sump I will be posting a build thread (Right now thinking custom GC 72 by 32 by 26).

Thanks!

 

[EnterName]

Disclaimer: I have not attempted this so I can only approach it from a theoretical perspective.

One of the biggest issues I can see with a "fully natural filtration approach" is that the phosphorus cycle doesn't work too well in reef tanks long-term. Carbonate surfaces do bind phosphate, but they dissolve most of it back once the water's phosphate levels drop again, so the rock and sand buffer phosphate rather than permanently removing it. That leaves water changes, harvesting macro algae, and a skimmer physically taking out particulate matter that contains phosphorus as the only means to export phosphorus (besides permanent growth like corals which is slower than the phosphate import).

Without a skimmer you will also reduce gas exchange, which is exactly the part of the carbon cycle that gets rid of carbon for you. You are limiting how much carbon dioxide can off-gas, and I can imagine you will notice this with lower pH readings sooner or later. We don't know too much about the organics in our tanks, but there is some evidence they play a role in cyanobacteria outbreaks, so it is in your best interest to have a decent carbon export, even if you are also carbon dosing to boost denitrification in the sand bed like Lasse does.

Additionally, all biological matter has to be fully broken down before the bound nutrients can exit the tank through the carbon and nitrogen cycle. A skimmer would remove particulate matter (containing C, N, and P) before those nutrients dissolve and become detectable by your tests.

"Biodiversity" is one of those terms that gets thrown around a lot, but as far as I can tell from AquaBiomics' observations it starts low in new tanks, builds over the first year or two as a tank establishes, and then older tanks tend to test lower again if you don't actively do something against it. You would need to continuously add live rock, sand, and mud to maintain biodiversity. Alternatively we might accept that biodiversity in a tank sounds really nice, but maybe it's not a requirement for a healthy tank as long as "the right organisms" have established. Otherwise tanks like mine that were started from 100% dry rock and sand, as well as very old tanks that haven't added any new live sources for years would struggle.

If you still want to try it, I would limit livestock to a minimum and get an absolutely oversized filter sump.

Edit: I'm not saying it's not possible, but it might prove challenging.

 

[shall72769]

But don’t corals need phosphate? Also I intend to harvest chaeto from my DSB fuge. I also plan to cure my rock in solution to remove as much phosphate as possible before starting the tank.

 

[shall72769]

And couldn’t the gas exchange problem be simply solved by a couple of air stones in the sump?

 

[EnterName]

But don’t corals need phosphate? Also I intend to harvest chaeto from my DSB fuge. I also plan to cure my rock in solution to remove as much phosphate as possible before starting the tank.

Yes, every living being requires phosphate (it's an essential building block of DNA so I'm not aware of any exceptions to this rule), but many people seem to introduce more phosphate into their tanks than the system can take up. Otherwise their phosphate readings wouldn't be above those of natural coral reefs which are somewhere around 0.005 - 0.03ppm iirc.

You have to remember that most of the phosphate that will be bound in your tank can redissolve, so it doesn't simply vanish. In fact, it still has an effect on your water: it shifts the equilibrium between bound and dissolved phosphate in your system. The more "phosphate-saturated" the calcium carbonate in your system is, the more phosphate is allowed to stay dissolved and therefore will be detectable by your tests.

Acid-treated rocks will give you probably quite some time, but can be a pain themselves. I had to dump insane amounts of monosodium phosphate solution into my tank to get the readings to 0.01ppm. The first corals introduced into that system didn't appreciate the lack of phosphate at all but fortunately still turned out fine.

I'm not saying it's impossible to keep phosphate low in your proposed system, but I still think it's important to be aware of the potential issues that will probably depend heavily on your choice of livestock.

And couldn’t the gas exchange problem be simply solved by a couple of air stones in the sump?

Air stones will certainly help (and might even be required to maintain oxygen levels in a tank that relies heavily on bacterial activity), but to get the same amount of gas exchange as a skimmer you will probably need quite a lot of them. I don't like using air stones because they cause so much salt creep and water-loss by throwing little droplets around on the water surface. At some point you might just go with a skimmer before turning your sump into a Jacuzzi.

 

[redfishbluefish]

The "two sump" part reminded me of the NatuReef system, but instead of it being a cryptic sump, it was an anaerobic sump. Note that this company is now out of business. Anyway, the second sump was a sealed acrylic tank with egg crate to support the growth of anaerobic bacteria. It came with a timer and pump, and water from your sump was pumped into this acrylic tank. Two mystery solutions were pumped in, one for nitrates (called something like NitraGone) and one for Phosphates (I can't remember the name). The nitrates would be converted into nitrogen gas and I don't know what happened to the phosphates. The Nitrate solution was based on methanol. After a period of time the pump would come on and empty this water back into you system while refilling the acrylic sump for it's next round.

Again, not cryptic, but a similar idea. Oh, and if you can find the chemistry on the two solutions, very easy to DIY the whole setup. This original system used an irrigation timer for the pumps to come on and off.