Sure, maybe substrates are the last thing we dream about when we’re planning our next big tank build. Maybe some of us quite frankly don’t put much thought into it at all. But in the end, when you’re snapping those full tank shots for Facebook, you might be surprised how much the color and even grade of your substrate can affect the look of your display. And, even more importantly, you might find that it has a substantial impact on both the short-term and long-term health of your 
system. While different aquarists have different budgets and goals, and may be attempting to recreate very different biotopes, there are a few substrates that are overall great in terms of appearance as well as function.
We here take a look at some marine aquarium substrates. The following are branded materials distributed by the old-school aquarium substrate giant CaribSea (Fort Pierce, Florida). All of these examples are extremely popular offerings from their ARAG-ALIVE!™ product line, namely Bahamas Oolite, Fiji Pink, Special Grade Reef and Hawaiian Black.
As “live” substrates, the ARAG-ALIVE!™ products are packaged slightly wet and are coated with live spore-forming bacteria. These microbes “come alive” and contribute to aquarium cycling as soon as the sand is emptied into the tank and biologically activated. Independent lab tests prove that ARAG-ALIVE!™ technology allows for faster cycling than with other substrates, including other live substrates.
Bahamas Oolite
Unlike all of the other substrates here listed, which are formed from the erosion of larger bits of rubble, oolitic sand is formed from the precipitation of calcareous materials in warm, shallow, highly agitated marine intertidal environments. Formation starts with a small fragment of sediment acting as a “seed” such as a miniscule shell fragment. Bahamas Oolite is excellent for use in deep sand beds (DSBs) where its extremely small grain size (i.e. high surface area) and low interstitial flow rates promote the growth of beneficial anaerobic bacteria. Moreover, it easily passes through the gills of sand-sifting fishes.
This sand is of a fine grade and high density at 0.25-1.0 mm diameter and 96 pounds per cubic foot. As such, it’s a great choice for a low flow (e.g. refugium and FOWLR) environment.
Fiji Pink
Don’t be expecting a solid, bright pink with this one. It’s more like… a blend of mostly beige with flecks of reddish and pinkish material. The overall effect, at least from a bit of distance, is a nice soft pink color. Its pale rosey hue makes it blend a bit more with coralline-encrusted live rock. If you prefer a light colored substrate, but prefer some colorful highlights (rather than pure white), then you’ll likely find this product to be extremely appealing. In fact, many hobbyists do–this has certainly been one of the top-selling substrates in the industry for quite a few years now!
This sand is of a fine-medium grade and somewhat high density at 0.5-1.5 mm diameter and 90 pounds per cubic foot. As such, it’s a great choice for a low-medium flow (e.g. LPS-dominated) environment.
Special Grade Reef
Here’s you classic reef aquarium substrate. It has an off-white color and a slightly chunky/flaky texture. For versatility and general use, you can’t go wrong with this stuff. Because it has a low content of fines, it is relatively more amenable to “gravel vacuuming.” It also works well as a thin, aesthetic covering on top of otherwise bare bottom tank floors.
This sand is of a medium-coarse grade and modest density at 1.0-2.0 mm diameter and 85 pounds per cubic foot. As such, it’s a great choice for a medium-high flow (e.g. mixed reefs) environment.
Hawaiian Black
This is definitely one of the more unusual substrates out there in terms of color. Mainly composed of darker material (with just a few flecks of whitish aragonite), it is reminiscent of the basaltic sea floors of volcanic islands such as those in Hawaii. Everything pops with this sand in the background, but tridacnid clams look especially gorgeous over it.
This sand features a relatively coarse grade and lower density at 0.25-3.5 mm diameter and 80 pounds per cubic foot. While there is a pretty wide range of grain sizes in this stuff, you could say that it’s almost graveley. As such, it’s a great choice for a high flow (e.g. SPS-dominated) environment. The roomy interstitial spaces between the substrate particle provides more living quarters to amphipods and larger copepods.
Conclusion
There are a lot of options out there when it comes to aquarium sand. But when it comes to looks, at least one of the above four options could appeal to just about any reef aquarist. Similarly, when it comes to function, these four present at least one good option for most applications. And yes, they can be mixed to suit a special look or job. When you consider that CaribSea guarantees a contaminant-free product and adds beneficial bacteria, these offerings from the ARAG-ALIVE!™ line look especially good!
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