Aquarium Substrates for Beginners
Quick Answer
Aquarium substrate is the material placed on the bottom of a fish tank. Common choices include gravel, sand, planted-tank substrate, and bare-bottom setups.
The best substrate depends on the fish you keep, whether you have live plants, how easy you want maintenance to be, and the appearance you prefer.
At a Glance
| Substrate Type | Best For |
|---|---|
| Gravel | Most beginner community tanks |
| Sand | Bottom-dwelling fish and natural-looking aquariums |
| Plant Substrate | Rooted live plants |
| Bare Bottom | Breeding, quarantine, and grow-out tanks |
| Crushed Coral | Raising hardness and pH when appropriate |
What Is Aquarium Substrate?
Aquarium substrate is the material covering the bottom of the aquarium.
It can provide:
- A natural appearance
- Support for live plants
- A surface for beneficial bacteria
- Areas for fish to forage
- Protection for the bottom glass
- A place to anchor decorations
Substrate is not required in every aquarium, but it affects the appearance, maintenance, fish behavior, and water chemistry.
Does Every Aquarium Need Substrate?
No.
Some tanks work very well without it, including:
- Breeding tanks
- Fry grow-out tanks
- Quarantine tanks
- Hospital tanks
- Some discus tanks
- Temporary holding tanks
Bare-bottom tanks are easy to clean and allow waste to be seen quickly.
However, many display aquariums look more natural with gravel or sand.
Common Types of Aquarium Substrate
Aquarium Gravel
Gravel is one of the most common choices for freshwater aquariums.
Advantages
- Easy to find
- Available in many colors and sizes
- Works well with gravel vacuums
- Supports beneficial bacteria
- Suitable for many beginner tanks
- Helps anchor decorations
Disadvantages
- Uneaten food can fall between the pieces
- Sharp gravel may damage bottom-dwelling fish
- Some plants do not root well in large gravel
- Waste can build up if it is not vacuumed
Choose smooth aquarium gravel rather than rough landscaping stone.
Aquarium Sand
Sand creates a natural-looking bottom and is often preferred for bottom-dwelling fish.
Advantages
- Gentle on barbels and soft-bodied fish
- Waste usually stays on the surface
- Natural appearance
- Good for burrowing fish
- Available in many colors
Disadvantages
- Can be drawn into filters
- May compact in deep layers
- Can cloud the water during setup
- Requires a different vacuuming technique
- Very fine sand may be difficult to rinse
Planted-Tank Substrate
Plant substrates are designed to support rooted aquarium plants.
They may provide:
- Nutrients
- Iron
- Minerals
- Better root growth
- Softer texture for plant roots
Some planted substrates can affect:
- pH
- KH
- Water clarity
- Ammonia levels during initial setup
Always read the manufacturer’s directions before adding fish.
Crushed Coral and Aragonite
Crushed coral and aragonite slowly release minerals into the water.
They may raise:
- GH
- KH
- pH
They can be useful for:
- African cichlids
- Livebearers
- Snails
- Hard-water aquariums
- Tanks with naturally low KH
They are not suitable for every aquarium. Avoid using them when you need soft, acidic water.
Bare-Bottom Aquariums
A bare-bottom tank has no gravel, sand, or soil.
Advantages
- Very easy to clean
- Waste is easy to see
- Useful for breeding and fry
- Good for quarantine and hospital tanks
- No trapped debris
Disadvantages
- Less natural appearance
- Fish may feel exposed without decorations
- Plants usually need pots or attachments
- Reflections from the bottom may bother some fish
How Much Substrate Do You Need?
The amount depends on the aquarium size and the depth you want.
A general starting point is:
- 1–2 inches for fish-only tanks
- 2–3 inches for many planted tanks
- Deeper areas where large rooted plants are used
Avoid making the substrate excessively deep unless the aquarium is designed for it.
A sloping substrate can create a natural appearance:
- Shallower at the front
- Deeper toward the back
How to Choose the Right Substrate
Consider:
- Fish species
- Bottom-dwelling fish
- Live plants
- Water chemistry
- Cleaning routine
- Aquarium size
- Desired appearance
- Cost
The most attractive substrate is not always the best choice for the fish.
Best Substrate for Corydoras
Corydoras spend much of their time searching the bottom for food.
Good choices include:
- Fine smooth sand
- Rounded fine gravel
Avoid sharp or jagged gravel that may damage their sensitive barbels.
Best Substrate for Kuhli Loaches
Kuhli loaches prefer soft substrate where they can dig and forage.
Suitable choices include:
- Fine sand
- Smooth small gravel
Provide hiding places such as caves, plants, and driftwood.
Best Substrate for Goldfish
Goldfish often pick up and move substrate.
Possible choices include:
- Bare bottom
- Sand
- Gravel too large to swallow
Avoid gravel that is just small enough to become lodged in a goldfish’s mouth.
Goldfish also produce a large amount of waste, so the substrate must be easy to clean.
Best Substrate for Bettas
Bettas can live with:
- Smooth gravel
- Sand
- Plant substrate
- Bare bottom
Avoid sharp substrate that could tear their fins.
Best Substrate for Shrimp
Shrimp tanks can use:
- Sand
- Fine gravel
- Plant substrate
- Specialized shrimp soil
The correct choice depends on the shrimp species and desired water chemistry.
Some specialized shrimp soils lower pH and KH, which may help certain soft-water shrimp but may not suit all species.
Best Substrate for Live Plants
Root-feeding plants often benefit from a nutrient-rich substrate.
Examples include:
- Amazon swords
- Cryptocoryne
- Vallisneria
- Dwarf lilies
- Rooted stem plants
Plants such as Anubias and Java fern do not need to be buried. Their rhizomes should remain above the substrate and can be attached to rocks or driftwood.
Can You Grow Plants in Regular Gravel?
Yes.
Many aquarium plants grow in regular gravel when they receive:
- Adequate light
- Suitable water
- Liquid fertilizer
- Root tabs when needed
- Proper planting depth
A specialized planted substrate can help, but it is not always required.
Should You Rinse Aquarium Substrate?
Most gravel and sand should be rinsed before use.
Rinse until the water becomes reasonably clear.
Do not use:
- Soap
- Bleach
- Household cleaners
- Detergent
Some planted substrates should not be heavily rinsed because rinsing may remove nutrients or break down the granules. Follow the product instructions.
How to Rinse Gravel or Sand
- Place a small amount in a clean aquarium-only bucket.
- Add water.
- Stir the substrate by hand.
- Pour away the cloudy water.
- Repeat until the water becomes much clearer.
- Add the substrate gently to the aquarium.
Rinsing smaller batches is usually easier than rinsing the entire bag at once.
How to Add Substrate to an Aquarium
For an Empty Aquarium
- Rinse the substrate if required.
- Add it to the empty tank.
- Arrange the desired slope.
- Place rocks and decorations securely.
- Add water slowly.
- Use a plate, bowl, or plastic bag to reduce disturbance.
For an Established Aquarium
Adding substrate to a tank with fish can create cloudiness and disturb waste.
Work in small sections and avoid burying fish, plants, or decorations.
In some cases, temporarily moving the fish may be safer for a major substrate replacement.
Can You Mix Sand and Gravel?
Yes, but the materials may eventually separate.
Larger gravel often rises while fine sand settles lower.
You can use rocks, wood, or barriers to create separate areas, but fish and maintenance may still mix them over time.
How to Clean Gravel
Use a gravel vacuum during partial water changes.
Push the tube gently into the gravel and allow debris to rise into the siphon.
You do not need to clean the entire substrate deeply every week.
How to Clean Sand
Hold the gravel vacuum slightly above the sand.
Waste usually sits on the surface and can be removed without pulling out much sand.
Pinch the hose or raise the siphon if sand begins moving too far up the tube.
Can Substrate Affect Water Chemistry?
Yes.
Some substrates can change:
- pH
- GH
- KH
- Mineral content
- Ammonia during startup
Examples include:
- Crushed coral raising hardness and pH
- Active planted soil lowering pH and KH
- Limestone-based gravel raising minerals
- Some soils releasing ammonia initially
Test the water after adding a new substrate.
Can You Use Outdoor Gravel or Sand?
It can be risky.
Outdoor materials may contain:
- Chemicals
- Pesticides
- Metals
- Limestone
- Sharp edges
- Parasites
- Dirt or pollutants
Aquarium-labeled substrate is the safest beginner choice.
Do not use beach sand without knowing exactly what it contains.
Can You Use Play Sand?
Some fish keepers use clean, plain play sand after thorough rinsing.
However, it may:
- Be very dusty
- Compact easily
- Contain varying grain sizes
- Take a long time to rinse
Avoid scented, colored, treated, or chemically altered products.
Can You Replace Aquarium Substrate?
Yes, but removing all substrate at once can disturb beneficial bacteria and release trapped waste.
A safer approach may be:
- Replace part of it at a time
- Keep the filter running properly
- Test ammonia and nitrite afterward
- Avoid replacing filter media at the same time
- Perform water changes as needed
For a complete replacement, move carefully and prepare for cloudy water.
Common Beginner Mistakes
- Choosing sharp substrate for bottom-dwelling fish
- Using gravel small enough for large fish to swallow
- Forgetting to rinse dusty substrate
- Making the substrate unnecessarily deep
- Burying plant rhizomes
- Using crushed coral in a soft-water setup
- Using active soil without checking its effects
- Cleaning the entire substrate too aggressively
- Using outdoor materials without testing them
- Replacing all substrate and filter media at once
Rick’s Experience
During my years keeping and breeding tropical fish and owning the FinTastik Tropical Fish store, I used different substrates for different purposes.
Breeding and grow-out tanks were often bare bottom because they were easier to clean. Display tanks usually looked better with gravel or sand. The correct choice depends on what you are trying to accomplish with the aquarium.
Frequently Asked Questions
Is gravel or sand better for beginners?
Both can work. Gravel is easy to vacuum, while sand may be better for fish such as corydoras and kuhli loaches.
How deep should aquarium substrate be?
About 1–2 inches is enough for many fish-only tanks. Planted tanks may need 2–3 inches.
Can substrate cause ammonia?
Some active plant soils can release ammonia during the first weeks. Test the water before adding fish.
Do beneficial bacteria live in substrate?
Yes. Beneficial bacteria grow on substrate surfaces, but the filter usually contains a large portion of the biological filtration.
Can I change from gravel to sand?
Yes, but work carefully, preserve the filter bacteria, and monitor ammonia and nitrite after the change.
Should I remove fish when adding substrate?
For a small addition, fish may remain in the tank. For a major replacement, temporarily moving them may be safer.
Is black substrate good for fish?
Black substrate can make many fish colors stand out and may help shy fish feel secure. It is suitable when the texture and chemistry match the aquarium.
Can substrate be too deep?
Yes. Very deep, compacted substrate can trap waste and develop areas with poor water circulation.
Rick Recommends
Useful substrate supplies include:
- Smooth aquarium gravel
- Aquarium sand
- Planted-tank substrate
- Root tabs
- Gravel vacuum
- Aquarium-only bucket
- Substrate divider
- Water test kit
Related Articles
- Aquarium Equipment Guide
- Aquarium Gravel Vacuums for Beginners
- Aquarium Water Quality Guide
- Understanding Aquarium GH
- Understanding Aquarium KH
- Live Aquarium Plants
Final Thoughts
The best aquarium substrate is one that suits your fish, plants, water chemistry, and maintenance routine. Gravel is a dependable beginner choice, sand works well for many bottom-dwelling fish, and planted substrates can support rooted plants.
Choose carefully before setting up the tank because replacing substrate later can be a major job.