Are Deep sand beds effective?

[LordJoshaeus]

I sure hope I posted this in the right part of the forum...anyhow, how effective are deep sand beds at removing nutrients? I did research on them and got VERY conflicting reports - some say deep sand beds worked wonders, others say they are useless, still others say they are nutrient traps. Here are the specifics of my plans; I was thinking of putting a 4 inch deep sand bed in the 10 gallon refugium of my 10 gallon non photosynthetic tank to encourage denitrification. The overflow is rated 550 GPH and the return pump is 350 GPH. I was also going to add bristleworms if I go the DSB route, and there was going to be an ENORMOUS (over two pints!) amount of macroalgae in the tank, chiefly Caulerpa sp. Thanks!

 

[Reeferdood]

The quick answer is they can be but there are other methods that work MUCH better than a DSB.
Learn about carbon dosing and if it is a method you might want to try.. I little Vodka goes a very long way towards nutrient export.

 

[jda]

They are fantastic at lowering nitrates once they get going - the anoxic bacteria populations can take a few months to establish. Where they fall down is misunderstanding and misuse. They seemed to work for most people for a handful of years and then the phosphate in the tank would start to rise. They were good at lowering nitrate for a long time. This got called "old tank syndrome" and many other things, but most people thought that they were releasing phosphate back into the water. This is not true... it is more complicated that this...

You have to understand how aragonite (sand and rock both) can bind massive amounts of phosphate from the water column. Hobbyists saw zero nitrate and very low phosphates and decided not to change water because they thought that they "did not need it." What was happening is that the sand was binding up all of the phosphate for quite some time and doing the job that the hobbyist was supposed to be doing with routine maintenance. Remember that there is a massive amount of aragonite here that can bind years worth of phosphates. What happened in about year 4 or 5 is that the sand got full and could not mask the lack of maintenance anymore and the phosphate levels started to rise to the point of inhibiting calcification, limiting algae growth (another false positive) and killing some types of coral. People did not understand why and the theories came out that a DSB is a "time bomb" or that the sand bed was "leeching" and some people abandoned their DSB.

The people who still did their maintenance or kept a fuge did not ever really have problems with their tanks.

Basically, the sand took the blame for the hobbyist.

I don't use a true DSB, but I do use about 3 inches. I like this because it will denitrify and I don't have to take up so much tank room with more sand. This is a safe way to lower nitrate and while it keeps mine very close to zero, it will not drive the nitrate too low with an overdose like Organic Carbon can - nature figures out the equilibrium and they are bosses at getting it right. I vacuum mine after year 3 or 4.... 25% a quarter for the next year. I also have conchs and a cucumber (that has split a few times) to keep it clean - they are fun to watch go to work. I change water and run a fuge and my phosphate levels stay low - with this approach the sand becomes a buffer for phosphate, not a reservoir.

What you are wanting to do is more of a remote DSB. If you add the word remote to this, then you can get all kinds of different threads. People liked these because they provided a safety net to just replace the sand without tearing down the tank to replace it. If you really want maximum denitrification, then look more towards 6" of sand.

 

[ca1ore]

May want to rethink caulerpa though …. its an invasive weed.

 

[LordJoshaeus]

May want to rethink caulerpa though …. its an invasive weed.

That's exactly why I want it...it's a nutrient sucking fiend.

 

[LordJoshaeus]

They are fantastic at lowering nitrates once they get going - the anoxic bacteria populations can take a few months to establish. Where they fall down is misunderstanding and misuse. They seemed to work for most people for a handful of years and then the phosphate in the tank would start to rise. They were good at lowering nitrate for a long time. This got called "old tank syndrome" and many other things, but most people thought that they were releasing phosphate back into the water. This is not true... it is more complicated that this...

You have to understand how aragonite (sand and rock both) can bind massive amounts of phosphate from the water column. Hobbyists saw zero nitrate and very low phosphates and decided not to change water because they thought that they "did not need it." What was happening is that the sand was binding up all of the phosphate for quite some time and doing the job that the hobbyist was supposed to be doing with routine maintenance. Remember that there is a massive amount of aragonite here that can bind years worth of phosphates. What happened in about year 4 or 5 is that the sand got full and could not mask the lack of maintenance anymore and the phosphate levels started to rise to the point of inhibiting calcification, limiting algae growth (another false positive) and killing some types of coral. People did not understand why and the theories came out that a DSB is a "time bomb" or that the sand bed was "leeching" and some people abandoned their DSB.

The people who still did their maintenance or kept a fuge did not ever really have problems with their tanks.

Basically, the sand took the blame for the hobbyist.

I don't use a true DSB, but I do use about 3 inches. I like this because it will denitrify and I don't have to take up so much tank room with more sand. This is a safe way to lower nitrate and while it keeps mine very close to zero, it will not drive the nitrate too low with an overdose like Organic Carbon can - nature figures out the equilibrium and they are bosses at getting it right. I vacuum mine after year 3 or 4.... 25% a quarter for the next year. I also have conchs and a cucumber (that has split a few times) to keep it clean - they are fun to watch go to work. I change water and run a fuge and my phosphate levels stay low - with this approach the sand becomes a buffer for phosphate, not a reservoir.

What you are wanting to do is more of a remote DSB. If you add the word remote to this, then you can get all kinds of different threads. People liked these because they provided a safety net to just replace the sand without tearing down the tank to replace it. If you really want maximum denitrification, then look more towards 6" of sand.

This is VERY helpful. Thank you!

 

[fredk]

...
What happened in about year 4 or 5 is that the sand got full and could not mask the lack of maintenance anymore and the phosphate levels started to rise to the point of inhibiting calcification, limiting algae growth (another false positive) and killing some types of coral. People did not understand why and the theories came out that a DSB is a "time bomb" or that the sand bed was "leeching" and some people abandoned their DSB.
...

What do you mean by "the sand got full"? Do you mean there was a build up of organics and refractory compounds?

I remember reading some scientific papers on phosphate binding on aragonite sands years ago and the ability to bind phosphate is very much pH dependent. It is possible for aragonite to release bound phosphate if the sand shifts from an alkaline to acidic environment. I don't remember the pH at which that shift happens any more though.

Sand beds are complicated environments and people had/have widely varying experiences with them. Some people had constant issue with organics building up in the sand bed. Some didn't. I suspect this is because the biological and chemical environments vary widely from one tank to the next.

 

[jda]

I mean that the structure of the aragonite could not bind much more phosphate. As a result, the tank phosphate goes up faster than it did before.

 

[Belgian Anthias]

The quick answer is they can be but there are other methods that work MUCH better than a DSB.
Learn about carbon dosing and if it is a method you might want to try.. I little Vodka goes a very long way towards nutrient export.

Carbon dosing does not remove nitrogen. A DSB does. Carbon dosing is not advisable for a new setup as a high C:N ratio may prevent the installation of a nitrifying capacity. DSB promotes denitrification. Carbon dosing promotes protein production. Adding Vodka does not remove a thing! Needs a skimmer to remove a part of the produced protein.

 

[427HISS]

jda-- "I don't use a true DSB, but I do use about 3 inches"

I'm planning a 125g and we like having gobies and other sand sifter's, will a 3" sand bed be enough for a effective, biological bed and food for pods etc,...and.for the fish ? Don't want a DSB of over 3".

 

[Reeferdood]

Carbon dosing does not remove nitrogen. A DSB does. Carbon dosing is not advisable for a new setup as a high C:N ratio may prevent the installation of a nitrifying capacity. DSB promotes denitrification. Carbon dosing promotes protein production. Adding Vodka does not remove a thing! Needs a skimmer to remove a part of the produced protein.

I can see you like DSB's whereas I do not, that is what is awesome about this hobby. I was not instructing the OP to use carbon dosing just to look at it as another means of nutrient export. BTW, carbon dosing works incredibly well & yes it must be used in conjunction with a skimmer...

 

[Pntbll687]

jda-- "I don't use a true DSB, but I do use about 3 inches"

I'm planning a 125g and we like having gobies and other sand sifter's, will a 3" sand bed be enough for a effective, biological bed and food for pods etc,...and.for the fish ? Don't want a DSB of over 3".

This should be ok.

I have 200lbs of sand in a 190. It's 4-5" deep in some parts and under an inch in others.

I will second the organic material gets "trapped" in the dsb. I wouldn't say trapped if the word, more like "isn't processed as fast as people think".

I do minimal water changes, but vacuum the sand once a month into filter socks too clean the top inch or two.

My advice would be to stay away from a dsb. If I could do it over again, I would go bare bottom with either a large fuge or biopellet reactor.

 

[jda]

jda-- "I don't use a true DSB, but I do use about 3 inches"

I'm planning a 125g and we like having gobies and other sand sifter's, will a 3" sand bed be enough for a effective, biological bed and food for pods etc,...and.for the fish ? Don't want a DSB of over 3".

The 3 inches that I have is fine to remove nitrate, feed about a dozen conchs and a cucumber that has divided a few times. In actuality, this means that most of the tank is 3 inches, but there are some spots that are 4" and some that are 2".

 

[jda]

I remember reading some scientific papers on phosphate binding on aragonite sands years ago and the ability to bind phosphate is very much pH dependent. It is possible for aragonite to release bound phosphate if the sand shifts from an alkaline to acidic environment. I don't remember the pH at which that shift happens any more though.

The amount of absorption is on a siding scale with pH, but still can be massive at any levels that we observe in a tank. I did an experiment and over 50 ppm of phosphate in 10g of water bound down to about .16 ppm with just a handful of the larger ARM calcium reactor media chunks.

The pH in the sand and inside of the rock is very stable since it is not really impacted too much by the co2 swings from photosynthesis. It is usually a bit lower than the tank. All evidence points to a stable environment where the binding happens, but I have never really seen a study that explicitly looks at this (we probably never will).

As an aside, I want to point out that people who uses silica sand for their sand bed have totally different experiences since phosphate binding nor buffering is possible here. Let's all just put these types of tanks off to the side since they are a whole different creature.

 

[hart24601]

We are in the era where if anything more problems are coming from people running too few nutrients in their systems. In the perspective of nutrient reduction clearly DSB are not needed as they are not used all that often now and alternative nutrient export work extremely well hence the nutrient additions!

But if one just enjoys them that is great, your tank is all about what you like! If that's the case then just follow the advice to keep it in good shape long term that has been given above.

If I was going to use dsb for export (I would use macro algae 1st but that's another story) I would use 2 five gallon buckets with bulkheads at the top above the sand line of course and valves before and after. Then after a couple years it's easy to replace one of the buckets by shutting the valve and disconnecting a union - and you have second bucket still colonized that you can replace later after the new bucket is running for 6mo or so. The number and size of buckets can be scaled to the system like rubbermaid stock tank.

 

[jda]

I do still consider this current state of keeping BUILDING BLOCKS higher is a trend that could very well reverse - not for all, but for many. I still like low, but not too low, levels of building blocks. However, my coral do have a ton of true nutrient from the sugars that the zoox provide with the high quality and high intensity lighting. Having a bit of sand helps keep my nitrate from .1 to 1 PPM and buffers phosphate around .01 PPM with other routine maintenance. There is also nearly no drifting of these levels. These levels are not growth inhibiting. Perfect, IMO. The nature takes care of most of this (other than water changes) and the bacteria and buffering adapt to the current demand to keep the levels there. I choose to let nature control this because it is their job and they do it like a boss... and way better than I would.

I think that the trend has been partially fueled by people thinking that N and P are nutrients and somehow feed coral. They are not. They do not. They are building blocks for life that are needed to make new organic tissue. You need some existence of these and they are very important, but after you have enough, then you do not need any more. Having more than ideal can inhibit cellular function and calcification after a while - different levels for different organisms. People are not feeing their coral more by having N and P levels rise - the hobbyist is not giving them more food. Coral get nutrients from the sugars that the zoox make, or by capturing carbon-rich food - which means that light is the most important factor in getting true nutrients to coral that they need for daily function as well as growing.

The trend is also fueled by people removing too many building blocks with artificial means. Having none is a huge problem. Having too many is WAY better than having none. I cannot blame people for adding too many if they had a period of time with none... but I think that they missed the sweet spot of having enough, but not too many.

Think of building blocks like this... when you want to brick the side of your home, you need a steady supply of a few bricks so that you can keep on mortaring them into place as you raise and expand the wall, but not too many at once. If somebody just filled your whole yard with bricks 20 feet deep, this would make getting the bricks put into place harder and nearly impossible. The sand bed can keep that slow and steady supply while not inhibiting calcification or cellular function of dinos - the sand can help create an environment with enough, but not too much. The sand will keep nitrate low by raising or lowering the numbers of anoxic bacteria to just keep the equilibrium driven. The sand will also bind and unbind phosphate to an equilibrium in the water... so if you go lower, then more is release... higher and it binds up more. The sand can basically do what people have been trying to figure out for years with GFO, organic carbon, LC, etc. It can keep doing it if you do not falsely think that your tank does not need maintenance. The only downside to this method is that it can take a year to fully establish all of these anoxic regions... and lots of people cannot wait a year anymore for anything.

 

[fredk]

...

The pH in the sand and inside of the rock is very stable since it is not really impacted too much by the co2 swings from photosynthesis. It is usually a bit lower than the tank. All evidence points to a stable environment where the binding happens, but I have never really seen a study that explicitly looks at this (we probably never will).
...

The paper I read did look explicitly at this, but it was in estuarine environments with much deeper sand beds than we can practically keep and much higher nutrient inputs. The result was a reversal in binding. and a cycling of phosphate back into the system. This is a very different environment than our tanks though.

I wish I had kept that paper. I could never find it again when I went looking.

To bring this post back on topic, I do remember someone on RC that had an external dsb filter where he fed water into the bottom of the bed via a series of pipes and drained water from the surface into his sump. He would vacuum the sand periodically to remove any organic build up. It worked quite well for him. In the end, I don't know if it would be easier to construct and maintain than an algal filter or not, but the algal filter will manage phosphates, at least to some degree, as well.

 

[hart24601]

Isn't nutrient by definition a substance essential for growth and maintenance of life? So in our context phosphate and nitrate are nutrients. No, they are not required in huge amounts beyond the typical suggestions, but they are essential.

 

[fredk]

...

I think that the trend has been partially fueled by people thinking that N and P are nutrients and somehow feed coral. They are not. They do not. They are building blocks for life that are needed to make new organic tissue. You need some existence of these and they are very important, but after you have enough, then you do not need any more. Having more than ideal can inhibit cellular function and calcification after a while - different levels for different organisms. People are not feeing their coral more by having N and P levels rise - the hobbyist is not giving them more food. Coral get nutrients from the sugars that the zoox make, or by capturing carbon-rich food - which means that light is the most important factor in getting true nutrients to coral that they need for daily function as well as growing.
...

The above paragraph leaves me puzzled.

Nutrients are compounds in foods essential to life and health, providing us with energy, the building blocks for repair and growth and substances necessary to regulate chemical processes

N and P fit into the definition of nutrients above and are no more or less essential than sugars. As pointed out in the quote above, you need essential nutrients for both repair and growth, so all organisms, including corals, always need them available for ingestion in some form or another.

All sugars are some form of carbon, oxygen and hydrogen in a specific ratio. Corals cannot get anything else from sugars. The carbon is for growth/repair. The oxygen, as far as I know, is just a nasty free radical that floats about looking for things to destructively bind to unless expelled from the coral. The hydrogen is used to generate energy at a cellular level.

Sugar is in no way some special 'true nutrient'. It has its specific purpose. Nothing more and nothing less.

 

[fredk]

...
All sugars are some form of carbon, oxygen and hydrogen in a specific ratio. Corals cannot get anything else from sugars. The carbon is for growth/repair. The oxygen, as far as I know, is just a nasty free radical that floats about looking for things to destructively bind to unless expelled from the coral. The hydrogen is used to generate energy at a cellular level.

...

Ok, now I'm mangling science. Sugars are one of the inputs to Krebs cycle of which byproduct outputs would be CO2 and H2O. Those nasty O2 free radicals come from photosynthesis. I swear, I really was paying attention in biology and chemistry, 40 years ago...

FYI, Krebs cycle also uses phosphate, so if your coral is using sugars, it needs P.

The overall point stands. Sugar is not some special nutrient to be elevated in importance above N or P.