Live Rock and Live Sand
At the first MASWA meeting I attended, it became apparent that not many attendees had had experience with live sand. Andy asked if I would write an article on it, as I have had live sand in my tank for about three years now. Live sand and rock are not that different in their bacterial processes, so to give a comprehensive explanation, it is necessary for me to include live rock in the story. In the following article, I will attempt to explain what live sand and rock are, their purpose and in my opinion, whether they are necessary or not.
What are Live Rock and Sand?
For me, the terms live sand and live rock have always sounded like a great way to add swarms of new and interesting unidentified animals to a tank. Unfortunately, if this is your intention, you will probably be disappointed with both types of live media because in reality, relatively few animals are included (although the number of animals on board does tend to vary from shipment to shipment). What they do contain though, is nitrifying and de-nitrifying bacteria.
Live rock and sand are usually dived for on coral reefs. The sand I have has been shipped from the Great Barrier Reef. It is also possible to obtain dead sand and rock from just about any source and over ti me, make them live. This will save money but may take a while and doesn't give any of the small creatures I mentioned above. The other drawback is that some types of rock and sand can be detrimental to you aquarium or inhabitants.
What do they do?
Obviously, as only occasional small animals turn up in live rock or sand, this is not the primary purpose of the two media. Fortunately for the live rock vendor, most people understand that the major purpose of live rock is to provide nitrifying bacteria and not animals. All but the absolute beginner will be aware that these bacteria are essential in our captive marine environments; they convert ammonia (NH4) into nitrite (NO2) and then into less harmful nitrate (NO3). For a lot of people, though, the purpose of live sand remains a mystery.
Live sand is relatively new in the marine aquarium hobby and became popular when it was discovered that, not only do the bacteria in live sand nitrify, they can also de-nitrify under the right conditions. That is, live sand converts NO3 to nitrogen (N2) and nitrous oxide (N2O) gas which then bubbles off into the atmosphere. Live sand has been touted as the simplest and most natural method of reducing nitrates in marine aquaria. One method of employing live sand is often called the natural nitrate reduction or NNR method.
How does this work? Well, if the layer of sand is the correct thickness (around 50-70mm), the bottom layers will become anoxic. This means that the oxygen levels are low, usually around 1ppm. To simplify the process, under anoxic conditions the bacteria take the oxygen atoms from the NO3 to use for energy conversion and this just leaves behind the N2 and N2O, which bubbles off to the atmosphere. Prior to the discovery of de-nitrification in live sand, it was known that live rock does the same thing within its core but it had not been considered efficient enough to take up the typically large quantities of nitrate in aquariums at that time.
A bit of history.
Midway this decade, the Berlin method became popular. It advocated no trickle filtration but instead lots of live rock and a foam fractionator (protein skimmer). The theory is that if a protein skimmer is used to filter the aquarium water, it will remove the majority of the organics before the proteins start to break down to ammonia and are further reduced by the nitrifying bacteria.
It is commonly thought that trickle filters will convert organics faster than a protein skimmer can remove them, but this is only partly true. The way that a trickle filter beats a protein skimmer is that it uses a pre-filter (and without one would itself become a pre-filter). The pre-filter traps the organics and here they break down to ammonia and are consumed by bacteria in both the dry section of the trickle filter and on any available surface in the aquarium. As the pre-filter organic trap produces such a large amount of ammonia (and, as bacte= ria colonise it, nitrite), the trickle filter is necessary because it harbours a large population of bacteria that will perform the oxidation fast enough. In affect, a trickle filter is a nitrate factory. Of course, if the organics are trapped in the pre-filter, there is no way that a protein skimmer can remove them. It will only take out the organics that haven't yet been trapped in the pre-filter.
During the trickle filter era, a substrate was not recommended. The reason was that the hobbyist had typically used a coarse substrate as a carry-over from the old under gravel filter days. Coarse substrates act as organic traps, as food and fish waste are likely to accumulate in them. Further, as more and more debris accumulates, the lower layers are starved of oxygen (anaerobic conditions) and hydrogen sulfide (H2S) is produced. H2S is deadly to marine fish and invertebrates. It is the black patches that can be seen some times in the shallows at the beach or if a large shell or rock that is sitting on your substrate is removed.
Are they necessary?
The short answer; no, they aren't necessary. But it seems that if you want to keep nitrates low in your aquarium, you now have more options, some of which will reduce your maintenance time. To begin with, if you don't have a protein skimmer, add one. Even if you leave your trickle filter attached, the protein skimmer will remove some of the organics. You could add a de-nitrification unit. These, in my experience, are either moderately expensive and fiddly or just damn expensive! The cheaper ones won't work in the presence of a protein skimmer. If you have an efficient protein skimmer, you can add lots of live rock and get rid of your trickle filter. It seems that if you have enough rock (about 2/3 of your tank), you will not need any live sand because the rock will do all your de-nitrification for you. Most reef hobbyists already have plenty of live rock and usually a protein skimmer so it is as simple as removing the trickle filter. If you have a protein skimmer but not a lot of live rock, you can add live sand as well. This, in my opinion, is the best method no matter how much rock you have. The live sand acts as a haven for microfauna, thereby producing food for your tank inhabitants and keeping the bottom of the tank clean. It also performs de-nitrification. A further advantage, if you are keeping anemones, is that sand may stop them from wandering. All you do is clear the sand from a spot on the bottom and allow an anemone to adhere to it. Once it has stuck, you can push the sand around the anemones base. This makes some (though definitely not all) anemones feel secure and ceases their endless search for a good spot to call home.
Things to watch out for with sand.
Is the sand dead or live?
If you get dead sand, it can take from 2 weeks to 2 months for bacteria to properly colonise it. If the sand is live, it has the bacteria in it and will also come with some animals such as burrowing worms, Cerith snails, sea cucumbers and brittle stars. All these animals help to keep the sand clean and turn it over thereby avoiding the formation of toxic H2S. This is especially useful if particularly fine grained sand is used.
What is the sand made of?
If you are collecting sand yourself, avoid silicate based sand such as local beach sand. This can leach silicates into your tank water and create a diatom bloom which will cover the tank glass and some invertebrates. Calcium based sand is best because coupled with bacterial activity, it will leach some trace elements and calcium into the tank water and help buffer your pH. If you are using dead sand, if possible get aragonite sand as this is considered best for calcium and pH maintenance. Aragonite is a mined sand and comes from ancient fossilised reefs. If you are getting live sand, then the best sand is, in order of preference (due to ease of calcium and trace element liberation), crushed Halimeda leaves, crushed coral and crushed shell.
Make sure you keep the grain size in mind. Having said this, in Western Australia we are usually at the mercy of the collectors and as most collectors have no idea as to what it is they are collecting, we generally have to just make do with what we get.
What size is the sand grain?
2mm sand is considered the best grain size. If it is much coarser than this, it can be difficult to move or damaging to sand stirrers and will also trap debris. If it is much finer than this, it is really silt and will not allow oxygen to diffuse through it and H2S will form. This may still be useable with the right sand stirrers. Some small pieces of rock (around 10-15mm) can be useful mixed with the sand as it helps burrowing animals such as Sleeper Gobies shore up their tunnels
Which is best, plenum method or plain sand?
For those of you who don't know, the plenum method (also called the NNR method, Jaubert plenum or erroneously, the Jaubert method consists of a vented, horizontal partition (like an under gravel filter) raised about 25-50mm off the bottom of the tank (this is the plenum) covered with a layer of fibreglass window screening, then a 25-50mm layer of coarse sand (3-5mm grain size), more screening and a 25-50mm layer of fine sand. The idea is that the plenum holds water which stops the level of oxygen from falling below 1ppm which is when H2S starts to form. The layers of window screening stop burrowing animals from getting down to the anoxic layers and allowing the oxygen level to go too high.
This method works well but in my mind is unnecessary, ugly, wastes space and is difficult to maintain as explained below: A 50-75mm layer of plain sand will de-nitrify just as effectively and, with the assistance of sand stirring animals, will not form H2S. Plain sand takes up less space and because of this, looks better and gives more room above for rock, inverts and fish. If an animal breaks through to the plenum, which is far from impossible, the whole sand bed becomes aerobic and can no longer de-nitrify.
When the sand dissolves due to bacterial activity and leaching into the water, it needs to be replaced. The fine sand will dissolve fastest but eventually the coarse sand will need to be replenished. When this eventuates, it is necessary to remove the remaining fine sand so that the screen can be lifted in order to add the coarse sand. If the live rock is on top of the plenum, which is very likely, then the whole tank will need to be de-constructed in order to do this. For this reason, some people are choosing to employ the plenum method in their sump only.
Well I hope this has been of help to everyone and if nothing else, at
least given you an insight to another method of keeping marine animals. =
If anybody would like further information, then you can reach me on: firstname.lastname@example.org
For a few pictures of my tank, look at the following site:
The Reef Aquarium: Volume 1 (J. Charles Delbeek and Julian Sprung, 1994, Ricordea Publishing)
Reef Notes Revisited and Revised: Volume 1 (Julian Sprung, 1995, Ricordea Publishing)
Sand Bed Systems by Sam Gamble (Aquarium.Net Cybermagazine February 1997 http://www.aquarium.net/0297/0297_7.sht)
Last modified 2006-11-24 18:41