Sand Substrate and the Nitrogen Cycle

An oft heard claim on the forum is that sand substrate is a suboptimal choice because of the potential for growth of anaerobic bacteria, which produce poisonous gases. This information most likely migrated from the world of fishkeeping, as many of us are involved in both hobbies.

Over the years, there has been a quiet revolution regarding the use of sand as a substrate for fish tanks. Reefkeepers employ the deep sandbed as a method of anaerobic filtration, which is beneficial for many invertebrates. Freshwater hobbyists have adopted the technique from reefers. As we have gained a better understanding of the science behind the (fishkeeping) hobby, it is clear that some of the dogmas were founded from a lack of information and fear of catastrophe.

I won't recite the nitrogen cycle in detail, but I'll stress that anaerobic bacteria are an important part of of the denitrification process in nature. As we know, ammonia (and sometimes urea) excreted from amphibians is initially oxidized to nitrite, by way of aerobic bacteria. From this point, nitrite can be further oxidized by different species of aerobic bacteria, converting it into nitrate. Nitrates accumulate in the aquarium, but are considered relatively less-toxic to fish and amphibians. We can deal with high nitrates by doing regular water changes. Therefore, we have adopted the view that aerobic bacteria are good, and anaerobic bacteria are bad for our tanks.

However, in nature, this situation is more complicated. After the nitrite is formed through oxidation of ammonia, anaerobic bacteria reduce (opposite of oxidize) nitrite to harmless nitrogen gas. Excess nitrogen escapes to the atmosphere via diffusion. Without this process, you would see the same build up of nitrates in natural settings. Through the reduction process, methane and sometimes sulfide gases are produced. The anaerobic colonies are visible as a dark layer in the sand, and are sometimes accompanied by methane bubbles. In nature, these gas bubbles are slowly released from the substrate, and they do not normally pose a problem to fish or amphibians. In the aquarium, it is feared that a giant bubble of methane will be released from the substrate and kill everything in it's path (as read by the movie preview voice).

What I want to explore is whether sand substrates are actually fostering anaerobic bacteria at densities required to harm amphibians in captivity. It seems to me that most of us maintain aquatic amphibians with at least some live plants, which limit the amount of nutrients processed by anaerobic bacteria. Also, we do regular water changes, do not keep the animals in crowded conditions, and have at least a bubbler to keep oxygen levels normal. So, who among us has had an amphibian suffer from conditions directly attributable to anaerobic bacteria in the substrate? Is the advice coming from experience or from fear?

It has been my experience that the deep sandbed provides a MORE stable environment, by allowing nutrients to be processed through multiple pathways, preventing the nitrite swings that can stress animals. However, this experience is based on fishtanks, as all of my newts remain in bare bottom tanks... Because I'm scared.

An interesting topic. I would love to see some scientific studies that sandbeds can cause the evil methane killer gas. I have employed the DSB in a reef tank with great success, and currently have a 3'' deep eco complete in my planted tank. I have not to this day experienced and catastrophies.

I am curious why no one in the freshwater/amphib world employs some sort of sand maintenance creatures. In the reef tank we employ various snails and such to keep the sandbed optimal. Nasarious (sp?) and ceriths to turn the layers of sand. Conchs and such to groom the top. Is there anyhting in the freshwater world that will dive down below the surface of the sand?

I've thought about using freshwater isopods for this purpose. I have had amphipods in culture, and they readily descended into the gravel substrate. However, I don't think either animal would have the same "turnover" effect in sand, like reef invertebrates do.

Well we will never know till we try it. Do you have a link or a species of isopod you are using? Same for the amphipod? I have got to believe that there is a worm or a snail out there that will readily survive in the temperatures we keep our tanks at that will process the layers of the same. While they may not be as efficient as a cerith or conch theoretically if there is an abundant food supply in the substrate they should multiply till they hit their equilibrium in supply of food. I am going to start looking into this. Not that I necessarily want a 5'' substrate or something of the sort but more for pure knowledge.

I have always enjoyed the substrate life in my reef tank. I always wondered why something similiar wasn't in the freshwater hobby. Not only is there potential nitrification that may benefit the tank. But it would also help potentially promote another live food source in the tank.

I need to think of how to set up the parameters of a few test tanks. Any ideas.

Any thoughts on using Melanoides tuberculata (Malaysian Trumpet Snail) to stir the substrate, or something similiar? I have seen various reports of the temperature ranges that are acceptable. I found one web site where 62F seemed acceptable, whereas another had 68F. I will dig for more potential species later.

I found in the past with sand substrates it is all about the depth of the sand, and how often you do proper tank maintenance.

Anything over an inch deep will, over time, develop the dreaded black sludge which releases gases. (Are these gasses methane? I have no idea, I find them unsightly either way...) The finer the sand, the more prone to this problem you will be.

Another factor here is lighting, as gases and anaerobic bacteria become more of a problem if algae growth coats the sand. This is especially dangerous as dying algae consumes oxygen resulting in a cascade effect of bad water chemistry.

While I am a huge advocate of "no substrate" this is because I am very lazy. Also, my skin gets contaminated with various industrial solvents and hydrocarbons from work daily. I try to avoid putting my hands in the tank as much as possible, even when they are "clean".

While I personally have not read of sand being "sub-par", I have seen many, many times sand used with stunning results. Proper use of a gravel vacuum attachment for your tank siphon, religious removal of uneaten food and feces, and the occasional good stirring up of sand substrates eliminates anaerobic issues.

As for the use of snails for keeping the sand churned up nicely, this does work however, many of those species get large enough to become a choking hazard to an axolotl. Remember, axolotls will eat anything that moves! Many of the others, while tiny are opportunistic feeders that have no qualms about snacking on your axolotl in swarms.
Another issue with burrowing snails is that even though they do a good job of churning up and feeding on the detritus in the sand, they do not eat their own waste, which is left in the sand. This provides good fodder for bad bacteria and can cause more chemistry problems than good. (I admit I am a bit biased against snails- I have had numerous problems with them in my axolotl tanks in the past and find them unsightly.)


To see the black sludge in action, take a good browse through the gallery here on the forums. There are also quite a few (in fact far more numerous) pictures of excellent sand tanks that show just how amazing this type of set up can be when properly maintained.

Well I suppose if you are concerned with the black look, you could go with black eco complete, or red eco complete, or even just red laterite. Personally I am not sure my cynops would look good against a black substrate, so I may opt for the pool sand. Red laterite is definitely out for me. I need to look further into this. As I am planning some heavily planted tanks for my cynops, which may make stirring the sand impossible.....

Hey,

last few months in Poland sandbes are more and more popular in freshwater tanks.
It is easly done with some of planning and thinking .
Here are photos:
http://www.akwarystyka.com.pl/showthread.php?t=50385&page=10

scroll down to photos of pipes, garden bars and some fabric.
On constructed this way passable for water shelves you put few coats of sands (the diameter of every coat is different and vary depending on method used by hobbyst).
As you can see there is a lot of water below heavy coats of sand - this is the place where live bacteries that do not need oxygen - it is the same process as in nature .

third post here: http://www.akwarystyka.com.pl/showthread.php?t=50385&page=11 show a drawning of a system.

here are photos from the begining of creating a system:
http://www.akwarystyka.com.pl/showthread.php?t=50385&page=27
sand have a smallest diameter.

next step: adding sand with bigger diameter, water, roots, etc
http://www.akwarystyka.com.pl/showthread.php?t=50385&page=29

black waters with sandbed filtration:
http://www.akwarystyka.com.pl/showthread.php?t=50385&page=45

You cannot use with this system big fish that love to dig for obvious reasons. You also cannot disturb sandbed too much because adding oxygen to this system will kill all bacteries which will be a disaster in an aquarium.

Regards.

Rick:
I haven't thought about the trumpet snails, though they may work. If I remember this species correctly, I'd be afraid that a newt would try to eat one. I wonder how much sand turnover is necessary?

Catfish dude:
The photo of the blackwater tank is awesome. Very mysterious.

Sludgemunkey:
Good comments. I hadn't included algae in the post, but they are certainly an important part of the nitrogen cycle. Apart from being unsightly, have your tanks experienced any negative effects from the "black sludge"? Edit: Don't take that to mean that I'm calling your tanks ugly

I like that blackwater tank as well! I have been contemplating setting up my tanks with false bottoms much like you see for dendros. This is much like the process catfish linked too. My reasoning is that I can create various levels of substrate without using deep sand beds. I will be able to plant aquatic plants such as java, crypts and alike and have a 1'' deep pool. As the newts become more aquatic I can start filling the tank and the plants will go aquatic leaving a nice scape. I am thinking instead of a waterfall I can return the water to below the substrate and use a spray bar to disperse and reduce the flow to a gentle flow. My biggest challenge will be to find an external pump that will give me a low enough gph to make the flow acceptable for the newts.

It was only 10 yrs ago when sand beds and deep sand beds were faux paux in a reef tank and look how that thinking has reversed. Now for many they are an integral part of the system and provide all sorts of micro fauna. My guess is the malaysian trumpet snails would not work as they do get bigger enough to be a potential hazard to a newt trying to eat one. My guess in the unique situation in keeping newts will require some sort of microworm or worm solution. I have started researching potential worms and have not come up with anything yet.

While this setup is not very good-looking it has been very functional for me. It's a ten gallon tank divided into barely submerged potting soil and deeper water by rocks siliconed in place. It has a sponge filter covered with commercial (avoid fertilizer, vermiculite, and perlite) potting soil. It houses two Xenopus frogs, one of which can be seen in the photo. There are both aerobic areas frequently turned over by the frogs, and anaerobic areas of substrate. The frogs are fairly heavily fed, mostly with freeze-dried tubifex worms. Partial water changes have been few and far between (months). The "aluminum plants" are periodically harvested by clipping. Nitrite and nitrate levels by APA test strips are indistinguishable from distilled water. Some functional denitrification is obviously occurring, either by uptake by the plants or denitrification by bacteria in the anaerobic portion of the substrate. Although this setup took a long time to cycle, it has been very stable since. One advantage of the setup for me has been observing the behavior of the frogs. They are often buried in the unconsolidated substrate, but when food is introduced they strike from ambush. They give the impression of stealthy and effective predators rather than the "go around and bite everything" feeding routine I have often seen in more conventional setups.

-Steve Morse

merk199 said:

Well I suppose if you are concerned with the black look, you could go with black eco complete, or red eco complete, or even just red laterite. Personally I am not sure my cynops would look good against a black substrate, so I may opt for the pool sand. Red laterite is definitely out for me. I need to look further into this. As I am planning some heavily planted tanks for my cynops, which may make stirring the sand impossible.....

Click to expand...

I think you may be confusing blackwater tanks with the black sludge that forms during anaerobic decay like this. Or perhaps I was unclear in what I was talking about.

What I was referring to as "the black sludge" is the build up of a dark colored substance under the substrate, often near the glass. This is organic decay caused by bacteria feeding on detritus in the absence of oxygen. This does result in the creation of gasses which bubble up through. Are they methane? I have no idea. I suspect folks that cry methane, may not truly know either.

While I am not saying the gasses are to blame, the rot itself is an indication of water chemistry issues and poor substrate maintenance. This invariably leads to other water related issues.


I will have to see if I can dig up some pictures of my old black water tanks for anabantoid fish....

My 300 gallon freshwater fish tank has a very deep layered substrate of (from top) gravel, topsoil, oak leaves, and more gravel. There is clearly a lot of activity going on in the substrate, as multicolored bands may be seen against the glass. Occasional bubbles of gas do rise from the substrate. Nitrate levels are negligible. The tank is planted, but nitrate levels were very low even before the addition of plants. I have lost no fish except a couple of jumpers.

I used the same setup on a smaller scale in my siren tank. The substrate is not as deep, and I cannot say whether anaerobic processes are taking place, but nitrate levels remain low there as well. The tank has a healthy crop of Nostoc between glass and substrate obscuring any possible sludge.

One of these days if I have the time and space I want to do some more rigorous testing of deep substrates and other non-traditional filtration methods.

A method I have not tried yet but which seems promising is the "phosphate reactor". This is essentially just a surface of some material with a sheet of tank water running over it, exposed to strong light. The constant supply of water, atmospheric oxygen, and light encourages vigorous algal growth; the algae pulls nutrients from the water to fuel its growth, including not only phosphates but nitrogenous wastes as well.

I am going to setup two tanks this weekend. A 10 gal and a 29 gal tank. It will have 1-1.5'' of organic topsoil, and then a layer of 1-1.5'' of play sand. This is similar to what is used in Diane Walstad NPT tanks. Of course the tanks will have plenty of plants. In my planted tank hobby no one seems concerned about the "dreaded gas bubbles." My guess is it is a myth but I guess we will see. Wish me luck!

I have a 20 gallon long aquarium with 3 adult triturus dobrogicus. I have a sand substrate. I would guess the sand is 1-2 inches thick. I have had no problems and I have had them in the setup for about a year without ever changing the sand. When I suck up the waste some sand comes with and over time I add some sand to it. When I initially set up the tank, I used a turkey baster just to sift threw it and release the trapped air.