Goby buried in sand
When starting up a new tank there are so many decisions to make and new trends to being introduced. The newest trend in the Marine hobby is to Go Back to Bare bottoms tanks. The last biggest trend were Deep Sand Beds and before that was Crushed coral. Each on of these systems have their advantages and their limitations.
Bare bottom tanks are the easiest tanks to keep clean and allow for very high levels of water flow in the tank. The principle behind bare bottom tanks is to have so much turbulent water movement within the tank so that nothing can settle on the bottom and all the debris will make it to the external filtration system to be removed before it has time to break down and produce ammonia, nitrites or nitrates within the system. The turbulent water is required so that there aren't any places in or under rockwork where debris is built up over time and causes the nitrate levels to increase within the tank. Live rock is employed as the major form of biological filtration and a very good protein skimmer is also used to keep the water as clean as possible. Bare bottom tanks are easier to maintain because it is very easy to see and remove debris that does fall to the bottom.
In order to get the required amount of turbulent water flow (Water Circulation) you need to employ powerful pumps and devices to change the water direction within the tank. External closed loop systems along with Turbel powerheads or SQWD's are the current preferences to create the required turbulence within the tank.
With a bare bottom tank, you stand a greater risk of having rocks fall on the bottom of the tank and breaking the glass or having the bottom of the tank crack because the weight of the live rock being carried on a few pressure points where the foundation of the rock sits on the glass instead of being dispersed throughout a substrate layer. This potential problem is being addressed by the use of something called Starboard. Starboard is a thin (1/2 inch) piece of acrylic material that is used for cutting boards and in some boats. This thin sheet of Starboard is sealed to the bottom of the tank with silicon to prevent debris from becoming trapped underneath. It will also absorb the impact of racks falling in the tank and disperse the weight of the rock more evenly across the bottom glass.
The bare bottom system isn't feasible for every tank. Some animals wont be able to handle the high currents required to keep debris in suspension such as seahorses. Other animals need the substrate to live in such as some anemones need to burry their foot to feel secure or tubeworms that prefer to burry the bottom of their tubes.
Crushed coral is composed of the skeletons of dead and dying corals that have been taken from the reef. Crushed coral is probably one of the easiest and cheapest substrates that can be found for a marine tank. This porous material is great to add to area for the beneficial bacteria to colonize and help with in processing the biological materials that fall to the bottom of the tank. The main disadvantage to crushed coral is that it can contain very sharp edges, which will be hard on bottom dwelling creatures, fish that filter substrates for food and small invertebrates that make their home within the substrate.
The depth of the crush coral that should be used will depend on the grade used. The larger the grade the less the depth should be for ease of maintenance since more debris could get trapped in the substrate. Since crushed coral is fairly heavy in nature it can handle turbulent water and high flow rates without being blown all over the tank.
Maintenance of a crushed coral substrate is fairly straightforward. Regular vacuuming is required as the larger particles will trap detritus and foul the water should it not be cleaned properly. It is also advisable to replace the crushed coral after a few years, as the pores will become clogged with decaying matter and will cease to contribute to biological filtration of the tank.
When the crushed coral is ready to be replaced there will be warning signs, such as excessive Cyanobacteria blooms that can't be controlled through the usual means, Hair algae will start to appear and nitrite levels will begin increasing within the tank. If these warning signs are ignored it could lead to poor unbalanced water quality and loss of life within the tank.
There are three different grades of crushed coral commonly available on the market.
The finest grade is generally found between 1 to 3 mm in size. This grade is good for reef tanks and can be used as a deeper substrate base and can even be used for a Deep Sand Bed. When purchasing this fine grade, take a close look at the material as it is commonly blended with crushed Puka shells. Crushed coral has a greyish-white colouration where as the crushed Puka shells will be pinkish in colour. The crushed Puka shells wont harm your system and will eventually dissolve, however they are very sharp and will be much more irritable for bottom dwelling creatures.
The medium grade is generally between 3mm and 9mm in size. This grade is good for reef tanks and with larger fish that like to dig. The particle size allows for small creatures such as bristle worms and amphipods to roam around in. Since there are a lot of open space between particles it's bet not to have too deep of a layer, up to 1.5 inches is plenty. Again, crushed Puka shells can be found mixed in with the crushed coral and caution should be used since these particles could easily cut into the mouth of a fish as they are digging.
The largest grade is generally used for fish only tanks where someone doesn't like the look of a bare bottom tank and has messy fish such as triggers, lionfish, puffers, angelfish and large wrasse. These particles are anywhere from 7mm to 30mm. A thin layer should be used and regular vacuuming is a must!
Aragonite sand is a calcium based substrate that is generally collected from tropical beaches. There are many different grain sizes available. The aragonite sand available in a LFS has been specially processed so that as many potential contaminants have been removed as possible. It can also be picked up in some stores that sell tropical play sand, however it is a riskier, albeit cheaper, way to go. The tropical play sand hasn't been cleaned and you run a risk of polluting your tank with unknown chemicals.
Since the sand is a calcium based substance, it has a limited capacity for buffering your water as it slowly dissolves in the lower portion of the substrate. It can also be used in Calcium reactors to help maintain calcium levels in heavily stocked reef tanks.
When adding it to a tank, it doesn't need to be rinsed. The micro particles are excellent for bacterial colonization and will dissolve fairly quickly, however it will initially cloud up the tank until enough bacteria grow on it to weigh it down. Water currents shouldn't be directed at the sand substrate as it will blow the sand around the tank fairly easily, softer indirect current should be used instead.
Aragonite sand also has a benefit of having smooth edges which makes it easy for small creatures to burrow through it and keep it stirred up.
When first starting out we hear a lot about live rock and live sand and often people question, what exactly is live sand? The primary definition of live sand is sand that has already gone through a cycle and has a sufficient amount of bacteria growing on it that it'll greatly reduce the amount of time that it takes for a tank to go through it's initial cycle. This means that it's already been sitting in a matured tank or has been collected from the ocean. The more live sand you can add the better a start your tank will have. Also if at all possible use a bit of sand from as many different sources as possible. This will make for a healthier more bio-diverse substrate.
The more extended definition of live sand will include the micro fauna that is generally found in a natural substrate that keeps the sand bed turning over like mini starfish, bristleworms, peanut worms, spaghetti worms, burrowing snails, mini crabs, brittlestars, etc. Without these sand bed creatures stirring up the substrate the sand will begin to clump together which greatly reduces the surface area of the sand bed, thereby reducing the surface area for the bacteria to grow on, and reducing the biological filtration in the tank.
A deep sand bed (DSB) is one of the most misunderstood types of substrate options available to a marine hobbyist. Originally they were touted as a magical no maintenance form of filtration and eliminating nitrates from the tank and the simplest things to keep, just add sand and go! Through the use of anaerobic bacteria, in a tank with a relatively small bio-load, the DSB is able to eliminate all traces of nitrates from the system allowing for optimum growth in fish, corals and invertebrates. As time progressed so did the experience understanding of what happens and what is necessary to keep one viable for any long-term usage.
A DSB is composed of a 4 to 6 inch deep layer of fine aragonite sand. The particle sizes should vary from the extremely fine dust to around 2mm. The different size particles allow sand-stirring creatures to be able to burrow through it and maintain tunnels that aid in water movement within the sand bed. The extremely fine particles are to help maximize the surface area for bacteria to colonize on. After the sand has been added to the tank, it's best to seed the sand with sand from an established tank or using live sand from the store. This live sand should not only have healthy bacteria colonizing it but should also consist of some micro fauna that is essential to the health of a DSB.
The micro fauna should consist of a wide assortment of small worms, amphipods, copepods, rotifers, mini starfish, and burrowing snails such as the Nassarius sp. The wider the variety of fauna you can add to the DSB and the larger the quantity available the better able the DSB will operate. It's important to regularly add a fresh supply of micro fauna to the DSB so the bed doesn't' become depleted and to supply new genetic material to keep the fauna healthy. Avoid keeping animals that will sift through the DSB, such as gobies and sand sifting starfish.
The job of the micro fauna is to twofold. First they break down the detritus in the tank into smaller and smaller particles making it easier for the bacteria to utilize, second is to keep the sand bed moving as they dig beneath the surface. This movement is vital to keep the sand from clumping together and to create small currents in the bed bring nutrients to the different zones within the DSB so that the nutrients can be utilized and to move the detritus down through the different zones in the DSB.
As the DSB matures different useful zones form. The two primary zones that are the most useful to use are the aerobic zone and the anaerobic zone. In the aerobic zone, bacteria convert ammonia to nitrites and then into nitrates. The anaerobic zone has bacteria that convert nitrates into nitrogen gas or ammonium, which rise back up through the layers where the nitrogen gas is released and the ammonium becomes food for the aerobic bacteria once again. Also during this process phosphates are released from the detritus and, in a fully functioning DSB, used by the fauna and bacteria as they grow and multiply, thereby cycling the phosphates within the DSB.
EEven though there are the two zones we are most concerned with it's important to note that in the absence of oxygenated water, a hydrogen sulphide zone will be created as well. Hydrogen sulphide is a very deadly substance that smells like rotten eggs when present. So long as this zone isn't disturbed it's nothing to be really concerned about, however if for some reason it does come too close to the surface or is otherwise disturbed then immediate action must be taken to remove it from the system. This can be achieved by a large water change and heavily oxygenating the water.
A lot of people run a DSB with a higher bio-load then it can reasonably handle. They were designed for SPS reef systems with only one or two fish and very light feedings. However since they were thought to be such simple things to use, they were quickly incorporated into all types of marine systems and that's when people started seeing the problems and limitations to the DSB. The heavier bio-loads sped up the time it took for the inherent problems to manifest.
As the fauna dig through the substrate the detritus slowly makes it's way down through the layers and goes through different processes of nitrate reduction until the inert mulm reaches the bottom of the tank. Unfortunately this can only happen for so long before your DSB fills up with mulm because there is no export system designed into the DSB concept. As the DSB fills up with mulm, the anaerobic zones start to move closer to the surface and there is less room for the fauna in the sand bed, eventually resulting in very little area for bacteria and fauna to utilize. With the reduction of bacteria and fauna, the organic phosphates that as been cycling within the system have nowhere else to go besides back into the rest of the tank.
This is the beginning of what is referred to as a DSB crash. As the phosphate levels slowly increase in the tank, Cyanobacteria and hair algae begins to appear, at first it can be removed and everything will appear to be fine, but the problem becomes persistent and slowly gets worse unless corrective action is taken.
Up until you start removing the Cyanobacteria and hair algae there is not way for the system to export anything. This problem can be delayed by siphoning the top layers of the DSB to remove as much debris as possible, by having a good protein skimmer on the system and by limiting the amount of phosphates and food that enters the tank. However, eventually your DSB will need to be changed.