Every saltwater aquarium needs a good substrate base. From "live sand" to crushed coral, there is a substrate for every purpose. Each has its own properties and can be used for different purposes. Here are the top substrates on the market today. Compare prices on the brand and type of sand that is best for you.
CaribSea Arag-Alive
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Calcium-rich aragonite marine substrate, packed with millions of heterotrophic, autotrophic, and chemolithotrophic bacteria. The bacteria population aids in waste reduction and reduces cycling time in new setups. Use alone or to kick-start dry aragonite. Arag-Alive marine substrate provides calcium, carbonate, and beneficial trace elements to help maintain pH and water chemistry without the constant addition of chemicals. 
Available in 4 grades and grain sizes:
Fiji Pink Sand 0.5-1.5 mm grain size.
Special Grade Sand 1.0-2.0 mm grain size.
Indo-Pacific Black Sand 0.2-5.0 mm grain size.
Hawaiian Black 0.1-3.0mm grain size.
CaribSea Aragonite
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This super-fine sand (0.2 to 1.22 mm grain size) is ideal for shallow static beds and bottom covering of up to 1" in depth. Also known as "oolitic" sand, this sugar-sized sand's fine round grains pass easily through the gills of gobies and other sand-sifting organisms.
CaribSea Florida Crushed Coral
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The only crushed coral with aragonite, which provides up to 25 times the buffering power of other crushed corals, dolomite, or oyster shell. Reportedly will eliminate chronic pH problems and provide maximum surface area for water purifying bacteria. Allows an increase in bioload by up to 50% and should never need to be replaced. Mixed grade with a grain size of 2.0 to 5.5mm.
CaribSea Seaflor Special Grade Reef Sand
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Seaflor Special Grade Reef Sand is a 1.0 to 2.0 mm diameter grain size of aragonite which is specifically engineered for plenum-type nitrate reducing beds or anywhere a deeper bed.
Nature's Ocean Bio-Active Reef Sand
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Bio-Activ Live Aragonite® sand and substrate mix quickly to remove ammonia, nitrite, and nitrate to stabilize your reef aquarium system. Also helps maintain proper pH and enhances buffering capacity. Each bag contains millions of live marine bacteria, including heterotrophic, autotrophic, and chemolithotrophic, preserved in their natural live state using a patented process and patented saltwater solution.
Available in 3 grades and grain sizes:
Reef Sand 0.5-1.7 mm grain size.
Reef Substrate 1.0-2.5 mm grain size.
Black Beach Reef Sand 0.5-1.5mm grain size.
Ocean Direct Caribbean Live Sand
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Ocean Direct Caribbean Live Sand is aragonite live sand with millions of nitrate-reducing bacteria. It reportedly ensures faster, safer initial cycling and better bio-filtration once established. This functional marine substrate increases buffering capacity of your aquarium.
Available in 2 grades and grain sizes:
Original Grade Substrate is, by weight, less than 1 mm in size (most of that are smaller than 0.66 mm). Oolite Substrate is almost exclusively sub 1 mm oolite (most of this will be less than 0.60 mm in size).
