To Sand, Or Not To Sand...

Choosing a substrate starts with the pretty basic question, “what is a substrate?” Briefly, substrate is whatever is chosen (or not) to cover the bottom of the aquarium. Over the years, the fad of the moment has changed several times in regards to how this should function and what your aquarium should look like. Today, there are really a lot of different materials available for the home hobbyist to choose from; from black sand to oolitic sand, live sand and rubble, what should one choose? This answer to this question has a few variables that need sussing out before a reasonable answer can be had. Some things you choose to keep will require softer materials, necessitating finer sand. Many aquarium critters don't require sand at all, and this is also a viable option.

Sussing that out further, do you even need a sandbed? If you ask our team here, you'll get different answers, and this makes sense. If you're keeping most wrasses, especially Halichoeres, Thallasoma, Pseudojuloides and Macropharyngodon genus fish, they need a relatively fine sandbed to sleep and hide in. Some corals seem to do better over sand than naked bottoms, like Trachyphyllia, Fungia and Wellsophyllia, though none of these actually require a sand bed. Some Heteractis and Macrodactyla anemones do best being able to attach their feet through a sandbed, and some clams seem to thrive in this arrangement as well. For many aquarists, the primary deciding factor is aesthetic; many hobbyists just like the look of a sandbed more than a bare bottom tank. It takes quite a long time for a bare bottom tank to get covered with coralline, but once they do, it is also a very attractive look, and likely less maintenance in the long term. The choice is yours.

Once you've decided on the animals you'll keep and if you need or want sand, then you get into the choice about what substrate to pick. The truth of the matter is, that like most things in an aquarium, there are lots of ways to succeed, and a few things to avoid. Almost all of the things to avoid can be managed with one simple tip: always buy your sand from an aquarium retailer, whether it is your Local Fish Store or an online supplier, this is an integral step to the long term success of your aquarium. This sand is free of contaminants, is composed of marine aquarium appropriate sand and sometimes is even biologically active. Upfront, this will be nominally more expensive than buying sandbox sand from a home improvement center. In the long term it will save you money to just do this job correctly the first time. The sand available for landscape use from these outlets is excellent for its intended use. However, there is no preference for what type of sand is used, or how clean it is. Most often, the sand available is silica based and will give you endless issues with diatoms (see diatom article). Home improvement sand also has no need to be free of contaminants, or nutrients and sometimes will even have added compounds to help it set up between and under pavers. The long term costs of trying to save money here are astronomical; it sets you up for failure and costs you time and money down the road. For those of you who live near the ocean, harvesting beach sand is usually illegal, and may be contaminated with nutrients and critters that you may not want in your aquarium.

Our recommendation is for you to use an aragonite based sand. These are natural ocean sands that are primarily made from natural processes as coral reefs and associated critters are broken down and renewed. When you walk down most tropical beaches, you're walking on aragonite sand. As you shop for sand your going to come across various sizes and colors. For the most part, color is preference based. What shade of white to pink are you going to want in your aquarium? You will also see black sand occasionally, and it will be marketed with a couple different names, usually it is called “Hawaiian Black Sand.” If you want to choose a black sand for your marine aquarium, just make sure you buy one that is 99% aragonite

In regards to grain size there are a few different categories. The finest category has a grain size between 0.25mm and 1mm. This sand is often called “superfine,” “oolitic,” and “sugar” sand. It is very fine, very soft, and very beautiful. The downsides of sand this fine is that it has a tendency to blow around in aquariums that have a lot of flow. It is generally expensive, and because the grain size is so small and can pack together so well, it takes more bags to get to a reasonable depth in the aquarium. It is nearly impossible to siphon without removing a substantial amount of it with the water.

The next size up is usually called “special grade”, “aquarium grade”, “medium grade” (and sometimes “fine grade”). This is our recommended size for most aquariums that choose to have or need sand. It has a grain size usually between 1.0mm and 2.0mm. It is fine enough to look natural and moves around a little, but has the weight to mostly stay put in flow levels high enough to help prevent detritus settling. It is more easily cleanable that the finer grades as it can be siphoned with a standard aquarium siphon. It will also take almost ¼ less sand to reach the same depth when compared to a finer grade. It is an excellent grade for keeping wrasses.

The next grade up is composed of large grain sizes, these generally have grain sizes between 2.0mm and 5.0mm. They are often called “Natural” and “Crushed Coral.” These grades are most useful in very large tanks that have extremely high flow. These substrates are intended to stay put in the flow levels that the most intense reef aquariums demand. The large grain size means they also require less sand to get the same coverage than either of the earlier two grades. Conversely, that same grain size attribute also means it is more prone to collecting detritus if enough flow is not provided. These same problems also apply to people using rubble as a substrate, which we do not recommend, save your coral rubble for your calcium reactor (another article – yes they are still relevant).

There is one final grade of sand that has a more specific application, and it is usually called “mixed grade,” or “original grade.” As the name suggests, this is a mix of sands and the grain will usually range from 1.0mm up to 5.0mm. It will also frequently contain chunks of crushed coral and even snail shells. This sand has a very natural look, and has the structural integrity that many burrowing organisms like Sleeper / Sifter Gobies, pistol shrimp, and some crabs require. It is also generally suitable for the needs of wrasses.

How deep should your sandbed be? Again, this is down to what are you intending to keep in the aquarium. As a general rule, for pure aesthetics, we would say you need between a half inch and an inch of depth. If you're keeping small wrasses, you will need between and inch and two inches. If you're keeping Sleeper gobies, or bigger wrasses, three inches should be considered a minimum.

There are also some water chemistry buffering effects and some filtration benefits to having a sandbed, though these can also be a detriment if the sandbed isn't maintained. Maintaining a sandbed is pretty straightforward. Sand should either be live and wet, or rinsed heavily before adding to the aquarium. This will keep your tank clear and avoid nutrient spikes (see our articles on setting up aquariums for more on adding sand). As a word of caution, very deep sandbeds can become anaerobic. This isn't a bad thing per-say, as some parts of nitrogen filtration require these conditions. However, we suggest you avoid this when possible, as these conditions can also start to generate some gasses that could be detrimental to your aquarium inhabitants. Our recommendation is that you avoid depths more than 4 inches deep. Sand should be vacuumed with your siphon during water changes, and stirred up regularly.

Lastly sand isn't permanent, its ability to absorb pollutants, and the buffering capacity it provides will both be lost, and even reversed in time. As a result, we suggest replacing your sandbed on a scheduled basis, at least every two years in lightly stocked aquariums, more often in densely stocked aquariums. To do this, remove your siphon from the hose during a water change and just use the hose to suck the sand out with the water change water. Replace the sand with rinsed or live sand and top up the water change. Never remove more than half the sand at a time. You can schedule this how you like, but we suggest removing all the sand over consecutive weeks water changes; half one week, half the next (or thirds, or quarters). This will leave your aquarium with plenty of biologically active sand to help re-seed the new sand, while still completely removing used sand over a few weeks.

We hope this little sand primer has answered some of your questions about what to do on the bottom of your aquariums. Now, head over to your local fish store, buy some sand, and tell them that Quality Marine sent you.