That is one of those controversial issues, like many other things in this hobby. Personally I believe it is hogwash. There are still folks that advise members not to use pool filter sand because it will compact and cause anaerobic pockets. But when you look at posts from other members, including myself who have set up tanks with pool filter sand, you will note that we have not suffered from anaerobic pockets or compaction, so that initself is proof that it is nothing but BS. And then about all those folks who set up Natural Planted Tanks using soil that have set up tanks for many years never to have experienced anaerobic pockets or compaction. If you have deep rooting plants that you plant, have snails to stir up the substrate, then it is a non-issue. In nature, this is likely what accounts for why you would not see it. A myrad of organisms that keep the mud aerated and some plants that give out very deep roots into the substrate which release oxygen and prevent the issue.

The biggest problem I see in this hobby is "parroting" vs "direct experience." Instead of testing or experimenting to confirm, people just believe everything they read and hear and then parrot it on forums. It makes my blood boil everytime I see it.

 

I am going to have to respectfully disagree with you Homer (for the first time). I use a sand substrate, and have used it for the last 4yrs or so, for my fish-centered tank and it does develop anaerobic bacteria. How do I know? If I skimped out on WCs or gravel vacs, it develops pockets of "air bubbles" near where the most detritus builds up and a certain type of green algae and/or BGA can begin to grow there. I have seen with my own eyes bubbles emerge from the substrate (this is not from the HOB). Sand tends to make it worse because it allows thicker pieces of detritus to form and get stuck deeper in the substrate without being dislodged with the filter current. This is also happening in my black sand substrate. But because the grains are very small, the detritus that forms within it has to be very fine itself. It hasn't accumulated as much as in my sand substrate, but I have occasionally seen small bubbles arise out of the substrate (this is not due to air trapped after WCs). The theory that roots will not allow anearobic bacteria to form is false or highly exaggerated. I used to have a huge watersprite plant in my sand substrate. It had roots that took up a 1/3rd of the tank from top to bottom. Anearobic bacteria grew there. Now, I'm not saying every tank will have anearobic bacteria, however, from my experience, it can happen. It is not myth or legend. One thing to note is that I completely erradicated the snails in the sand aquarium. My black sand substrate has a few I believe. Take from that what you will.

 

Well, thanks for that info, homer.

 

Lol, no thanks needed. It is just my take on the issue. You have set up some absolutely beautiful tanks using mud with an overcap of sand. Have you experienced compaction or anaerobic pockets? My guess would be no, cause you started many of those emersed and had good deep root growth right off the bat.

 

The only problem I have had with anaerobic bacteria was my first tank setup. It was a 55gal with an under ground filter. Bad news, with around 5in of substrate in some places it didn't take long until the filter was nothing but a sewer. Once I changed over to a canister filter and added some Malaysian trumpet snails I've never had any more problems. But I didn't use sand just plain gravel.

 

I have also observed pockets of anaerobic substrate in aquariums, especially with finer grained sands. I knew that this was the case because I could detect the rotten eggs odor of hydrogen sulfide (H2S). While this gas is extremely toxic, it is also extremely smelly, so even trace amounts can cause a strong oder. I did not see any effect on the aquarium fish.

Anoxic sediments can most definately occur in nature. The rotten eggs smell that you get from sticking a canoe paddle in deep mud on a lake bottom is also created by H2S. Some aquatic plants can't grow at all in anoxic sediment, while others are uniquely adapted to use such substrates.

 

yes, I'mm sure that it will grow, but will it really hurt the fish? I have gone to the lake and seen huge bubbles come out of the lake bottom. The fish seemed fine.

 

Sometimes catastrophes do happen. Nature tends to fill in the gaps.
Occasionally, iIf you read lots of news reports, you will see that most or all the population of some small village has been killed by a huge gas bubble that rose to the surface of the lake the village is next to. The gas pours out of the water displacing Oxygen asphyxiating people and animals.

 

If you do a little more digging, this is due to volcanic activity, not anaerobic pockets.

 

I use the ol' anaerobic bacteria excuse all the time around my house....

"Don't look at me...must have been the tank again...."

.

 

Good question.

I keep asking those Power sand zealots, the heater cable zealots the same things...............

Never have ever gotten a straight answer.

Go figure.

In answer to your specific question, it very well can be a huge issue, or not.
The main thing driving the anaerobic nature in sediment is carbon, the reduced organic kind, you know........carbs, fats etc, same stuff we eat for energy.

Bacteria consume is so fast, the O2 is depleted.
So this is the central cycle in sediments that are flooded. There's a massive amount of research and peer reviewed articles about this single topic.

If you have no organic matter, the sediment can be 10 ft thick, the O2 will be the same ............It's a biology question, not an engineering question. That's marketing gets the folks who do not know any better(zealots and belief).

You have to have a certain amount of redox to get anaerobic conditions, they just do not appear out of the thin air. These are defined by bacteria and organic carbon.

Then............this is not the rest of the story............we have plants.
They add a lot of O2 to the root zones and they have all adapted to well to flooded soils..............they use a few methods, but most use channels to pump O2 to these sediments where they naturally grow.

Again, why folks skip this part(plant's effect), and focus soley on engineering is beyond me. Insane.

Some aquatic plants can't grow at all in anoxic sediment,

Okay, you brought this up, name one aquatic plant, that cannot grow in such a sediment? Entertain me.

I've only had anaerobic sediment(black H2S) pockets where a rotting Aponogeton bulb was placed, or due to no CO2/really really poor plant health (plants, melting, slowly dying etc)

Bubbles alone could be and are also from aerobic sediments, generally CO2. Just like us.

Bubbles alone do not imply anaerobic conditions.
Plants and good growth, imply good sediment O2 supply, regardless of the particle size, this pathway is never resistricted since it's inside the plant, not defined by the physical characters of the grain sizes.

If you do not look at the plant's role here and their influence, you miss a huge part of the ........cough cough...........planted tank.
Be careful in how you look at this. This stuff is not opinion, it's very well studied and they have many text books and research papers on wetland soils with and without plants.

Cables and powersand ARE NOT part of any natural system.
So they are not studied, however, the general models and relationships used for wetland soils are very well studied.

R. Reddy's latest book(2008) is certainly the best text on the subject as it addresses plants, wetland anaerobic soils, cycling of each nutrient, etc.
If you want to learn about sediments and how they interact with soil, then you should read this book if you wish to learn more. Then you also will know how to test the system to see if the effects are significant and how to do this for aquatic plant tanks as well.

Regards,
Tom Barr

 

All substrates are anoxic within 48 hours of being flooded. Soils within 24 hours. Anaerobic processes are necessary for some nutrient release from soils. Aerobic processes contribute in a different way. Anoxic pockets that resist being turned aerobic by plants are usually dominated by anaerobic bacteria that are feeding on compounds containing sulfer, which is where the hydrogen sulfide gas comes from. This gas is poisonous to aerobic critters (which includes plants). If the plants are doing well however, they can beat back the anoxic bubble and get roots set. It is the daily interplay in the plant root's rhizosphere between oxic and anoxic conditions that promotes the aerobic and anaerobic processes that make nutrients available for uptake by the roots.