Do deep sand beds really help remove nitrates?

[chimmike]

Just a thought, but key to a nitrate reducing DSB is the slow but sure advection of water through it. You need water movement and some corresponding pressure differentials at the surface of the DSB - advection enough to bring nitrate laden water to the anaerobic areas, but not so much as to prevent the anaerobic areas in the first place. Right?

So the idea would be to have a maybe a volume of water flow over it with a permeable "slot" towards the bottom of the DSB to allow water through (but prevent sand migration) ala some coffee filters or something that wouldn't degrade?

 

[Oceansize]

If you're looking at DSB's because you're looking for an efficient, low-maintenance method of nitrate export, I'd like to humbly offer my alternative experience because it has been very positive for me.

I've come into reefing relatively recently and so was able to consider both old-school and new-school methods of nitrate-to-nitrogen gas conversion when planning my tank. I'm admittedly lazy when it comes to water changes so I was really looking for something as efficient, consistent, and low maintenance as possible. DSB's seemed too inconsistent/impossible to adjust export rate, fuges seemed like they belonged in sumps which I don't have space for, and biopellets also seemed to cause many people a lot of grief trying to figure out, or turning out to be more maintenance than expected (pellets gumming up the works, etc).

I don't have enough experience to know if those experiences are truly representative (so nobody flame me, m'kay?), but they were enough to cause me to keep looking for a different method. Additionally, I scuba dive and I know that one of my favorite types of reef fish I've encountered on those dives are gobies/blennies, and when I heard I couldn't have them with a DSB, I immediately stopped considering DSB as a possibility.

That was when I discovered sulphur denitrators. It's basically a reaction chamber just like a calcium reactor, but simpler because there is no CO2 tank or controller to mess with. The chamber is filled with sulphur pellets and a little bit of aragonite. Once it is cycled, it is pretty much maintenance-free, aside from keeping an eye on the drip rate coming out of it every once in awhile and replenishing the sulphur every one or two years.

It is extremely efficient, has a small footprint, requires extremely low maintenance/monitoring, and you can adjust your nitrate level to something more than zero if you want by adjusting the efficiency of the denitrator. Basically its a small reaction chamber that you can put anywhere and mostly forget about it, no sump, no pellets. Yes I am a huge fan of my denitrator!!

I find it hard to understand why they aren't more popular, aside from their relative new-ness on the scene, at least here in the States (the tech was first tested in Europe somewhere between 10 and 15 years ago if memory serves).

My point simply is, if the subject is nitrate export, you may want to look into sulphur denitrators before making a final decision. The one I use is the Korallin S-1502, I'm assuming I'm not allowed to post a link to it, but it gets 4.5 stars at marine depot.

 

[Newb73]

It seems to me that super high flow circulation and frequent water changes will result in a much cleaner tank than allowing this extremely slow and extremely inconsistent biological degradation process to be a source of nutrient removal.

That said, I have some deep mud in my refugium and the way my pumps have blown my sand aroubd, I have areas that are 5 plus inches deep (and some areas that are bare bottom).

 

[chimmike]

I'm looking at DSB, refugium, and algae scrubber to go with as natural a filtration system as I can. I don't want to (but will probably) run all sorts of reactors and fancy skimmer for nutrient export/control. Nice refugium with some mangroves, deep sand bed with burrowing snails, and algae scrubber should be fairly effective.

 

[CastAway]

I think it may be debatable, and surely a topic somewhere here on R2R, but I question the effectiveness of mangroves for nutrient export in aquariums.

I also wonder about anything "burrowing" in a DSB, oxygenating what you don't want oxygenated.

More than I am desiring of nitrate reduction, it's the micro fauna in a DSB that I want. Free coral food.

 

[ReefMadScientist]

I have a DSB and DO have a Diamond Goby and two Sand sifting stars. I never had any issues with my DSB. I also gravel vac maybe once a month when I do my monthly water change.

You want to reduce Nitrate? Cut down on how many fish your tank has and feed more rationally.

 

[Randy Holmes-Farley Verified Community Expert]

I think it may be debatable, and surely a topic somewhere here on R2R, but I question the effectiveness of mangroves for nutrient export in aquariums.
.

I agree. They may be a nice addition, but they typically grow quite slowly relative to other organisms such as turf algae or macroalgae. So if you want them to be a significant nutrient export, you need quite a few for most tanks.

 

[CastAway]

My logic was, well, how can nitrates get deep enough in the sand bed to be effected by anaerobic bacteria if it isn't supposed to be able to penetrate such depths in the first place.

Also, I gather that one can have the same benefit of a dsb by creating a dsb in the sump and a thin bed in the tank.

Detritus and nitrates are not synonymous. Although detritus may not penetrate below the surface of a DSB, nitrates will. In my relative ignorance, this is the idea behind fine grains and depth, it keeps detritus on the surface for detrivores and decomposition, and a colony of anaerobic bacteria below in the undisturbed yet permeable fines. If there is no advection of water through the bed the process fails. If the deep portion of the bed is disturbed, say by a goby or vacuuming, the process is impeded if not stopped altogether as oxygen is increased in that disturbed area. Might be cool, might not cause a "problem", but it's not denitrifying.

I run a shallow coarse bed in the display, and a 5-6" fine bed in the sump. Without removing the DSB altogether however, I have no clue as to its effectiveness or efficiency. :-(

 

[chimmike]

How would one create advection through a DSB aside from just hoping it occurs?

 

[CastAway]

So the idea would be to have a maybe a volume of water flow over it with a permeable "slot" towards the bottom of the DSB to allow water through (but prevent sand migration) ala some coffee filters or something that wouldn't degrade?

Yeah. There is the "flow" of water through the area where the DSB resides, which should be relatively small. Much debated and dependent on volume, perhaps 3x the system volume per hour. But then there's turbulence in the area over the DSB, which is what results in the advection of water through the bed. Myself, I aim for enough flow so as not to disturb the surface of the bed.

There's some great reading on the topic in Delbeek & Sprung's The Reef Aquarium Vol 3., Science, Art and Technology.

 

[CastAway]

How would one create advection through a DSB aside from just hoping it occurs?

Besides the laminar flow through the sump and over the DSB, I use a small Ehiem skimmer to increase the water movement in the area.

Crappy pic, but....

 

[chimmike]

Last DSB I had was between the main tank drain and the skimmer chamber, so the full cycle flow ran over the DSB at all times. Did not disturb the sand. Come to think of it, I had a chunk of LR in there and some cheato.

What about some slots towards the bottom of the DSB on the discharge side, with some sort of membrane to prevent sand movement, but allow water in the deeper portions either from flow through the top and downward or otherwise?

 

[CastAway]

Last DSB I had was between the main tank drain and the skimmer chamber, so the full cycle flow ran over the DSB at all times. Did not disturb the sand. Come to think of it, I had a chunk of LR in there and some cheato.

What about some slots towards the bottom of the DSB on the discharge side, with some sort of membrane to prevent sand movement, but allow water in the deeper portions either from flow through the top and downward or otherwise?

Here's my sump and DSB area - I may have the "slots" you're describing. I didn't need any membrane other than some egg crate to prevent macro from getting pumped into my DT.

 

[chimmike]

So your DSB went higher than the level of the open, I'm gathering? Any current photos?

 

[CastAway]

So your DSB went higher than the level of the open, I'm gathering? Any current photos?

No, DSB surface is below the openings. Not a recent pic, but here it is with the bed in place, but before the tiny skimmer. What you're describing is more of a plenum system, like an "undergravel" filter. Not sure that would work. I think it would clog. I don't think you can make it out, but in this picture I have made rows in the DSB surface, like a garden. They provided enough disruption in flow as to create those tiny pressure differentials and resulting advection of water through the bed. A rock here or there would do the same thing. Now however, I just rely upon the skimmer/power head, and am thinking of adding a second. Hope I have not hijacked this thread. :-(

 

[KWSanders]

all this discussion about nitrate removal and then others add stump remover ( potassium Nitrate ) to fertilize the symbiotic algae in their coral .

 

[aviationreef]

I was thinking about adding a DSB onto my Display refugium i am making, i have heard good things about them and also very bad things.

 

[s2nhle]

It is depend on what type of coral you are keeping. SPS required clean water. LPS and soft corals could tolerate a little dirty water.

 

[aviationreef]

So you are saying a DSB will cause a nutrient level higher then sps corals can stand?

 

[chimmike]

I don't think a DSB makes the water any 'dirtier', what we're debating is the effectiveness of it neutralizing nutrients.