How To Guide: Choosing an Aquarium Substrate
Gravels, Sands, & Soils-- Oh My!
When setting up a new tank, you're faced with a multitude of choices when it comes to aquarium substrates. Each brings its own set of characteristics, like grain size, color, nutrient content, and even impact on water chemistry. These options may seem daunting at first, but fret not! We've gathered all the essential information to streamline your decision-making process so that you can set up your tank with confidence. Here are the key considerations to guide you in selecting the perfect aquarium substrate:
Which Livestock Will You Keep?
The living creatures in your tank may require a particular environment in order to be happy and healthy, so you should ensure your substrate choices will promote their wellbeing. Many species are able to tolerate and adapt to a range of evironmental conditions, but there are some that require specific considerations. A few examples are listed below.
Bottom-Feeders, Sand-Sifters, and Burrowers
- Catfish (Banjo, Corydoras, Glass, Pictus, Whiptail, etc.)
- Plecostomus / Plecos (Common, Bristlenose, etc.)
- Loaches (Clown, Kuhli, etc.)
- Ropefish
- Shrimp
- Snails
There are several species that spend the majority of their lifetime on or near the bottom of the tank, sifting through substrate looking for tasty morsels. For these types of fish and invertebrates, it's important to select a smooth substrate that will not cut or injure their delicate bodies as they go about their daily business.
Look For: Smooth river rocks, pebbles, rounded gravel, smooth-grained sand, soft aquasoils.
Avoid: Any gravel with sharp edges or rough sands made from shell fragments.
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Alkaliphiles (African Cichlids, Live Bearers, etc.)
- Mbuna, Peacock, and African Butterfly Cichlids
- Lake Victoria Cichlids
- Shell Dwellers
- Guppies
- Platies
- Swordtails
- Mollies
Many livebearing fish and African Cichlids prefer harder water with an alkaline pH (above 7.0). If the water you intend to use in your aquarium is very soft and/or low in pH, then you may want to consider using an active substrate.
Active substrates influence water chemistry by releasing or buffering certain substances, helping to create and maintain specific conditions in the aquarium. Common types of active substrates include those which influence the nutrient and mineral content of water (i.e. aquarium soils), those that are designed to buffer or stablilize pH and hardness, and those that include beneficial microorganisms which contribute to aquarium start up and the nitrogen cycle.
To foster an alkaline environment, use active substrates containing aragonite, crushed corals, or crushed limestone. These will help increase and maintain pH, GH, or KH in your tank, providing optimal conditions for your alkaline-loving (AKA alkaliphile) fish.
If you are unsure of the pH or hardness (GH and KH) levels in your aquarium, you need to test them before using an active substrate. If your water is already hard and alkaline, then using an active substrate may increase levels beyond what is recommended or desired, potentially harming your livestock. For aquariums that already have sufficient pH and water hardness levels, an inert substrate is best. Inert substrates are those which do not significantly alter water parameters.
Look For: Any inert gravel, rock, or sand. If increasing pH & water hardness is needed, opt for active substrates including aragonite, crushed corals, shells, or limestone.
Avoid: Acidic pH buffering substrates, soil-based substrates (including aquasoils), or anything containing volcanic ash, peat, or similar nutrients marketed for planted tanks
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CaribSea Super Naturals - Jelly Beans (Inert) |
CaribSea Original African Cichlid Mix (pH Buffering, Water Hardening) |
CaribSea Eco-Complete African Cichlid Sand (pH Buffering, Water Hardening, Live Bacteria) |
Acidophiles (Discus, Caridina Shrimp, etc.)
- Tetras (Cardinal, Neon, Rummy Nose)
- Angelfish
- Discus
- Apistogramma Cichlids
- Hatchetfish
- Corydoras Catfish
- Pencilfish
- Amazon Swords
- Java Ferns
- Caridina Shrimp (Crystal Red, Cardinal, Taiwan Bee, etc.)
Acidophiles are organisms that thrive in acidic (below 7.0 pH) environments. There are several fish, plants, and invertebrates that fall into this category that are popular amongst freshwater aquarists. When choosing substrate for an aquarium housing these species, it could be helpful to opt for one with buffering capacity designed to soften the water and maintain pH levels at or below 7.0.
As in the case of alkaliphiles, you would need to first test your water parameters to determine whether a buffering substrate is the right choice for you. If your water is already slightly acidic and soft, then using this type of active substrate could deprive your plants of necessary minerals and create harmful water conditions for your fish.
Look For: Any inert gravel, rock, or sand. If lowering pH & water softening is needed, opt for aquasoils and other buffering substrates containing volcanic ash, peat or similar compounds.
Avoid: Alkaline pH buffering substrates. Any substrate made from crushed shells, corals, limestone, aragonite, or similar. Gravel from stones known to leach minerals into the water column, such as marble.
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Brightwell Aquatics FlorinVolcanit (pH Buffering, Water Softening) |
(pH Buffering, Water Softening) |
CaribSea Samurai Shrimp & Plant Soil (pH Buffering) |
Which Plants Will You Grow?
Now that we've discussed fish and invertebrates, let's dive into a few substrate considerations for planted aquariums. Outside of aesthetics, the substrates you choose for a planted tank will be based on which live plants you intend to keep.
Root Feeders
- Swords (such as Amazon Swords)
- Cryptocornyes (aka "Crypts")
- Vallisneria (ex: Jungle Val)
- Aponogeton
- Lily plants
- Sagittaria
- Echinodorus
Root-feeding aquarium plants primarily absorb nutrients through their root systems rather than relying on nutrients dissolved in the water column. These plants typically benefit from nutrient-rich substrates in order to flourish and thrive. Inert substrates such as gravel can also be used with success, but you will need to regularly add root tabs, which are fertilizer tablets inserted directly into the substrate designed to release essential nutrients over time. It's important to note that even mineral-dense soils formulated specifically for plant growth will still need to be supplemented with root tabs once they are exhausted of all their nutrients, but that may not happen for 6-24 months depending on the rate of plant growth in your tank.
Substrates comprised solely of small particle sizes, such as silt or very fine sands, should be avoided due to compaction issues. The fine particles can pack tightly together, making it difficult for plant roots to spread and limiting oxygen exhange, water circulation, and nutrient absorption. Large gravel or rocks allow for increased circulation and oxygenation but can hinder the establishment and growth of plant roots. Many aquarists prefer to use graded substrates (i.e. containing multiple particle sizes) in order to reap the anchoring benefits of fine particles while avoiding the issue of compaction.
Look For: Aquasoils and other soil-based substrates, nutrient-dense substrates, planted tank specific blends, graded substrates (i.e. mixed particle size), and root tabs to supplement if using inert substrates
Avoid: Extra-fine sands, inert substrates (unless supplementing with root tabs)
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(pH Buffering, Water Softening, 3-5mm Particles) |
CaribSea Eco-Planted Substrate (Live Bacteria, 0.25-7.0mm Particles) |
(pH Buffering, Water Softening, 5mm) |
Water Column Feeders
- Anacharis
- Hornwort
- Water Sprite
- Duckweed
- Java Fern
- Anubias
- Frogbit
- Salvinia
- Water Lettuce
Column-feeding aquarium plants primarily absorb nutrients directly from the aquarium water through their leaves and stems, so they do not require nutrient-rich substrates in order to thrive. If your aquarium is mainly comprised of stem plants, epiphytes, and floaters; then you may want to skip the excessively nutrient-dense substrates and just use liquid fertilizers as needed. Substrates marketed for planted aquariums are still useful, as the nutrients will leach into the water column over time, but they are not necessary.
When it comes to stem plants, the best particle size is usually a medium grain to allow for proper anchoring and water circulation. A particle size too fine may suffocate roots, whereas too large may lead to easy uprooting during initial planting and regular maintenance, although the latter issue can be easily solved by using planting baskets. Also keep in mind that many stem plants have delicate roots that may be damaged when planting into excessively coarse or sharp substrates (also easily solved by using planting baskets).
Look For: Medium or graded particle size, naturally mineral-rich gravels, soft or smooth textures, and liquid fertilizers to supplement if using inert substrates
Avoid: Excessively nutrient-dense aquasoils, excessively fine sands or silt, coarse substrates with rough or sharp edges
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CaribSea Super Naturals - Midnight River (Inert, 1-4mm) |
CaribSea Super Naturals - Peace River (Inert, 1-2mm) |
(Mineral-Rich, High Porosity, 1-8mm) |
Carpeting Plants
- Dwarf Baby Tears
- Monte Carlo
- Micro Sword
- Marsilea Hirsuta
Carpeting plants in freshwater aquariums are low-growing plants that spread across the substrate to create a lush, carpet-like appearance. They often have high nutrient requirements, so a nutrient-dense substrate that also supports healthy rhizome or stolon structure is the path to success. Because they have delicate root systems that spread horizontally underneath the substrate surface, it's important to avoid excessively large or coarse grained substrates that may damage or impede root growth.
Look For: Small to medium particle sizes around 1-3mm, nutrient-dense substrates, aquasoils, smooth or soft textures. Add root tabs or nutrient-dense bottom soil if opting for inert gravels and sands.
Avoid: Coarse substrates with rough or sharp edges, excessively large particle sizes that obstruct root expansion
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(pH & KH Buffering, ~1mm) |
(pH Buffering, Water Softening, Live Bacteria, 1-3mm) |
CaribSea Super Naturals - Torpedo Beach (Inert, 0.5-2mm) [Use w/ root tabs or on top of nutrient-dense soil] |
Mixed Needs, High Tech Tanks, & Pro-Scaping
There may be scenarios in which you need to combine multiple substrate options to achieve your particular planted aquarium goals. Substrates can be combined or layered in different ways to accomodate a variety of plant and aquascape design needs. You can use different substrates for different areas of your tank, or take a layered approach to ensure the best substrate is available at the appropriate root level for each species of plant you intend to grow.
If you're running a high tech tank with many heavy root feeders, fast growers, optimal lighting and CO2 injection; you are probably going to want a layered substrate approach that includes one or more highly nutrient-dense base layers with some type of "cap" layer on top to prevent excess nutrients from leaching into the water column and causing algae growth or ammonia spikes. This is a more advanced approach with endless possible combinations, but it's really not necessary for beginner level planted aquarium keeping. If you choose to go this route, be sure to do your due dilligence in research and follow manufacturer instructions carefully.
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(Base Layer or Standalone, Active) +
(Top Layer or Decorative, Inert) |
(Base Layer, Active) +
(Top Layer or Standalone, Mineral-Enriched) |
Brightwell Aquatics FlorinBase Laterite Powder + (Base Layers, Active) +
Brightwell Aquatics FlorinBase Laterin Substrat F (Base Layer or Top Layer, Active) |
Other Considerations
Once you address the needs of your livestock and plants, the rest becomes a matter of preference.
Maintenance Preferences
Rocks, pebbles, and gravel will be easier to clean regularly with a siphon or gravel vacuum. Fine particle substrates like soil and sand may cloud the water during maintenance, and can even clog filters and pump impellers if not careful.
Aesthetic Preferences
Some people just like the look of one substrate over another. If your heart desires a planted aquarium with multi-colored neon gravel, then go for it! Just be sure to add a nutrient-rich base layer or root tabs to give your plants the best shot at success.
Speedy Start Up
Some substrates, such as Fluval Bio-Stratum, and CaribSea EcoPlanted & EcoComplete, include live bacteria to help kick start your aquarium cycle. This is an added benefit that could save you time and money during the new tank start up phase.
Experience Level
If you're brand new to the hobby, you may want to stick to inert substrates with root tabs until you have a better understanding of water chemistry and your particular aquarium's needs. Using a high nutrient soil inapropriately could cause more algae problems or ammonia spikes in a new tank.
Cost
Specialized aquarium soils can be more costly than gravel or sand; however, you can offset the cost by mixing or layering different substrates.
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