What should you put on the bottom of your aquarium? Is there a benefit to having substrate that is super fine versus something more chunky? What about no substrate at all? We will take a look at these options and you can decide which works best for you. At Tidal Gardens, we run a bunch of separate systems, some that feature substrate and others that do not. Depending on what you are trying to accomplish with your tank, one option might more make sense than another.
A bare-bottom tank has no substrate whatsoever. It is easier to clean because detritus collects on the bottom of the tank and can be removed easily. The problem with a bare-bottom design is there is little room for neglect. A bare-bottom tank must be siphoned regularly to avoid unsightly piles of detritus from forming.
Is bare bottom right for you? Let’s see.
The first thing that comes to mind is it’s a great solution for hobbyists who want very strong flow in their aquarium, such as SPS-heavy tanks. Bare-bottom tanks avoid the risk of strong currents kicking up the substrate and creating a sand storm.
The second benefit avails itself if one can keep up with the maintenance: it’s possible to maintain a laboratory-clean system with practically a mirror finish on the bottom of the tank. Aside from this aesthetic, long-term accumulation of detritus can cause older aquariums to break down as their processing capacity is exceeded. Regular removal of detritus goes a long way towards preventing this.
Aragonite Sand Beds
Most reef aquarium substrates are ground-up aragonite, which is a crystalline form of calcium carbonate. There are three major benefits of a substrate like this. First, it is aesthetically pleasing, or at the very least more natural than a bare-bottom tank. This is an aesthetic-driven hobby, so one might argue that it is the single most important criteria for reef keepers when deciding on a substrate.
Second, substrates are capable of biological waste processing. Microfauna such as worms and copepods grow in the sand and do wonders for nutrient control. In our bare-bottom systems, we see huge accumulations of detritus that need to be taken out. In our systems with crushed coral, the substrate hides the detritus and processes the waste. We even have a system that never gets attention, and it is flourishing. The corals are growing on top of one another. That said, the capacity of the substrate isn’t infinite, and one day a major reboot may be necessary.
Third, the nature of aragonite helps buffer calcium and alkalinity levels to a small degree. Over time, the substrate dissolves–similar to reactor media in a calcium reactor–and releases calcium and carbonate ions back into the water.
So, is this substrate good for what you are trying to do? Crushed coral (as opposed to sand) is great for aquarists that are looking for a more natural aesthetic yet still want relatively strong flow in their aquariums. The weight of crushed coral keeps the substrate from blowing around.
Second, some types of fish require a coarse substrate such as engineer gobies and jawfish.
Third, a coarser substrate is better for snails. I’ve seen some snails struggle to right themselves or even move across sand that is too fine.
Fine Sand Substrate
So when would a finer substrate be preferable? I’ve found fine substrates a good fit for low-flow systems such as refugiums with heavy macro algae growth. Due to the fineness of the sand, it actually helps keep the detritus on top of it, unlike larger grain aragonite substrates that trap it inside. Fine sand is also good for sand sifting diamond gobies, and wrasses that burrow at night.
To wrap things up, there are pros and cons of each type, so your choice is really going to depend on what you are trying to do with your system. Factors such as aesthetics, frequency of maintenance, and the dynamics of the aquarium such as flow rates all play a part in what makes for the best substrate for your particular system.
Than is the owner of Tidal Gardens and Advanced Reef Aquarium. Than's background is a mix of biology, computer science, business, and law. However, the reef aquarium hobby eventually led him away from a suit and tie corner-office job to pursuing his passion growing coral and shooting underwater videos.