Aquarium Substrate Guide: Gravel, Sand, and Soil Selection

Substrate—the material lining the bottom of your aquarium—is far more than decorative. It anchors plants, houses beneficial bacteria, affects water chemistry, and influences fish behavior. Choose wrong, and you’ll battle algae, struggling plants, or unhappy fish for years.

This guide covers every substrate type, their best uses, and how to select the perfect foundation for your specific aquarium goals.

Why Substrate Matters

Biological Filtration:

Substrate houses beneficial bacteria colonies
Processes waste and maintains nitrogen cycle
Deeper substrates (2+ inches) support anaerobic bacteria
Reduces nitrate in established tanks

Plant Growth:

Anchors root systems
Provides nutrients (in fertile substrates)
Affects root oxygenation and health
Determines which plants can thrive

Fish Behavior:

Bottom-dwellers need appropriate substrate
Some fish sift sand through gills
Substrate color affects fish coloration
Natural behaviors depend on substrate type

Water Chemistry:

Some substrates alter pH and hardness
Can buffer water parameters
Affects nutrient availability
Critical for sensitive species

Aesthetics:

Frames your aquascape
Affects perceived brightness
Complements or contrasts with hardscape
Creates the “feel” of the environment

Substrate Types Deep Dive

1. Aquarium Gravel

Standard Aquarium Gravel:

Size: 2-5mm pebbles
Colors: Various (natural, neon, painted)
Cost: $5-15 per 10 lbs
Best for: Fish-only tanks, beginners

Pros:

Easy to clean with gravel vacuum
Good water flow through substrate
Anchors plants reasonably well
Excellent for undergravel filters (if used)
Inexpensive and widely available

Cons:

No nutrients for plants (requires root tabs)
Uneaten food falls between stones
Sharp edges possible (check quality)
Can trap debris if not cleaned

Plant Compatibility:

Root-feeding plants need root tabs
Stem plants and rhizome plants fine
Carpeting plants struggle

Fish Compatibility:

Good for most fish
Corydoras prefer smoother gravel
Avoid with fish that swallow substrate

Recommended Brands:

CaribSea Peace River (smooth, rounded)
Estes Marine Sand (ultra-fine gravel)
Natural river gravel (tested for safety)

2. Aquarium Sand

Play Sand (Pool Filter Sand):

Size: Fine (0.5-1mm)
Color: Natural tan/white
Cost: $5-10 for 50 lbs (very economical)
Best for: Cichlid tanks, beginners on budget

Black Diamond Blasting Sand:

Size: Fine to medium
Color: Black
Cost: $8-15 for 50 lbs
Best for: Dark themed tanks, highlighting fish colors

CaribSea Super Naturals:

Size: Various
Colors: Multiple natural shades
Cost: $15-25 per 20 lbs
Best for: Premium aesthetic, planted tanks

Aquarium-Specific Sands:

CaribSea Aragonite: For marine/cichlid (buffers pH)
CaribSea Eco-Complete Planted: Pre-cycled, nutrient-rich
Fluval Stratum: Plant-specific (technically soil)

Pros of Sand:

Natural appearance
Fish can sift through it (natural behavior)
Debris sits on top (easier to clean)
Excellent for bottom-dwellers
Corydoras and loaches love it

Cons of Sand:

Can compact (reduces oxygen)
May develop anaerobic pockets (rare with proper depth)
Harder to plant in than gravel
Can cloud water if disturbed
Requires careful cleaning technique

Plant Compatibility:

Stem plants root well
Rhizome plants (Anubias, Java Fern) fine
Root-feeders need root tabs
Some carpeting plants struggle

Fish Compatibility:

Excellent for: Corydoras, loaches, goldfish, eels, cichlids
Avoid with: Large fish that swallow substrate

Maintenance:

Hover siphon just above sand (don’t plunge deep)
Stir surface weekly to prevent compaction
Don’t clean all at once (preserve bacteria)

3. Aquasoil and Plant Substrates

Commercial Aquasoils:

ADA Amazonia:

Type: Premium aquasoil
Benefits: Nutrient-rich, lowers pH, excellent plant growth
Cost: $30-50 per 9L bag (expensive)
Best for: High-tech aquascapes, serious planted tanks

Fluval Stratum:

Type: Volcanic soil
Benefits: Nutrients, plant-friendly, affordable aquasoil
Cost: $20-30 per 8.8 lb bag
Best for: Planted tanks, beginners to aquasoil

UNS Controsoil:

Type: Premium aquasoil
Benefits: Clean, consistent, plant-optimized
Cost: $25-40 per bag
Best for: Aquascaping, planted community tanks

CaribSea Eco-Complete:

Type: Volcanic rock substrate
Benefits: Pre-cycled bacteria, some nutrients, dark color
Cost: $20-25 per 20 lb bag
Best for: Planted tanks, dark substrate preference

Pros of Aquasoils:

Contains nutrients plants need
Promotes robust root growth
Lowers pH slightly (good for plants/fish)
Long-lasting fertility
Dark color enhances fish colors

Cons of Aquasoils:

Expensive
Can cloud water initially (rinse carefully)
Lower pH may not suit all fish
Depletes nutrients over 1-2 years
Hard to clean without disturbing

Plant Compatibility:

Excellent for: All plants, especially root-feeders
Required for: Demanding carpeting plants
Benefits: Cryptocoryne, Sword plants, stem plants

Fish Compatibility:

Fine for most fish
Some aquasoils soft (avoid large digging fish)
Perfect for shrimp and nano fish

4. Dirted Tank Method (Soil + Cap)

Setup:

Bottom layer: Organic potting soil (1-2 inches)
Top layer: Gravel or sand cap (1 inch)
Creates nutrient-rich base at low cost

Best Soil:

Organic potting soil (no fertilizers, no manure)
Mineralized topsoil (dried, sifted)
Commercial aquascaping soils

Pros:

Extremely cost-effective ($10 for large tank)
Very fertile for plants
Long-lasting nutrients
Excellent plant growth

Cons:

Initial setup messy
May cloud water for days/weeks
Can release ammonia initially
Requires research and patience
Not suitable for fish-only tanks

Best For:

Experienced aquascapers
Heavy planted tanks
Low-tech setups
Budget-conscious planted tanks

5. Specialty Substrates

Crushed Coral/Aragonite:

Purpose: Raises pH and hardness
Best for: African cichlids, livebearers, brackish
Cost: $15-25 per 20 lbs

Peat:

Purpose: Lowers pH, creates blackwater
Best for: Soft water species, discus, apistos
Form: Granules or placed in filter

Laterite:

Purpose: Iron-rich clay additive
Best for: Planted tanks (under other substrate)
Use: Base layer under gravel

Calcium Carbonate Sand:

Purpose: pH buffering for marine/reef
Best for: Saltwater tanks, African cichlids
Example: CaribSea Aragonite

Active Substrates (Buffering):

ADA Amazonia: Lowers pH to 6.0-6.5
Fluval Stratum: Slight pH reduction
Crushed Coral: Raises pH to 7.5-8.5

Substrate Depth Guidelines

Fish-Only Tanks:

Minimum: 1 inch
Recommended: 1-2 inches
Purpose: Aesthetic, minimal bacteria housing

Planted Tanks (Low-Tech):

Minimum: 2 inches
Recommended: 2-3 inches
Purpose: Root growth, bacterial colonies

Planted Tanks (High-Tech):

Minimum: 2 inches
Recommended: 2-3 inches
Purpose: Nutrient-rich base for root feeders

Deep Sand Beds (DSB):

Depth: 3-4+ inches
Purpose: Anaerobic bacteria reduce nitrate
Risk: Hydrogen sulfide pockets (rare with proper maintenance)

Sloped Substrate:

Front: 1-2 inches
Back: 3-4 inches
Purpose: Creates depth, taller plants in back
Technique: Use rocks/foam as terraces

Substrate Calculators

General Formula:

Substrate Volume = Tank Length (in) × Width (in) × Depth (in) ÷ 231 = Gallons needed

Weight Estimates:

Gravel: 1 lb per gallon per inch depth
Sand: 1.5 lbs per gallon per inch depth
Aquasoil: Varies by brand (check bag coverage)

Quick Reference (2-inch depth):

10-gallon tank: 20 lbs substrate
20-gallon tank: 40 lbs substrate
40-gallon tank: 80 lbs substrate
55-gallon tank: 110 lbs substrate

Buying Extra:

Always buy 10-20% more than calculated
Allows for sloping/terracing
Extra for adjustments or future use

Substrate by Tank Type

Community Fish Tank

Best Options:

Smooth gravel (2-3mm)
Pool filter sand
CaribSea Peace River

Why: Easy maintenance, good for most fish, plant-friendly with root tabs

Planted Tank (Low-Tech)

Best Options:

Fluval Stratum
CaribSea Eco-Complete
Dirted tank (soil + sand cap)

Why: Nutrients for plants without CO2, supports root feeders

Planted Tank (High-Tech)

Best Options:

ADA Amazonia
UNS Controsoil
Fluval Stratum

Why: Rich nutrients, lowers pH for CO2 injection, optimal plant growth

African Cichlid Tank

Best Options:

Aragonite sand
Crushed coral
Texas Holey Rock with sand base

Why: Buffers pH to 7.8-8.5, natural for Rift Lake species

Discus/Soft Water Tank

Best Options:

ADA Amazonia
Sand with peat moss
Bare bottom (breeding)

Why: Lowers pH, softens water, natural Amazon feel

Goldfish Tank

Best Options:

Smooth gravel (too large to swallow)
Sand (fine enough to pass through)
Bare bottom (easy cleaning)

Avoid: Small gravel (choking hazard)

Shrimp Tank

Best Options:

Dark aquasoil (ADA, Fluval Stratum)
Fine gravel
Sand

Why: Biofilm growth on aquasoil, dark colors enhance shrimp colors

Breeding Tank

Best Options:

Bare bottom
Very thin sand layer
Marbles (egg-scattering fish)

Why: Easy to clean, easy to see eggs/fry, no debris accumulation

Installation and Setup

Preparation

Rinsing:

Gravel: Rinse until water runs clear (5-10 minutes)
Sand: Rinse extremely well (15-30 minutes) to prevent cloudiness
Aquasoil: Do NOT rinse (destroys beneficial properties)
Soil: Mineralize and dry if making dirted tank

Testing:

Place questionable stones in bucket of water
Test pH and hardness after 24 hours
Check for fizzing with vinegar (carbonate rocks)

Layering Techniques

Single Layer:

Pour substrate directly into tank
Spread evenly with hand or cup
Slope from front to back if desired

Dirted Tank Layers:

Bottom: Soil (1-2 inches, moistened)
Cap: Gravel or sand (1 inch minimum)
Mist soil to settle before adding cap
Fill extremely slowly to prevent clouding

Planting Pockets:

Create small depressions in substrate
Fill with aquarium soil or root tabs
Cover with main substrate
Plant directly into enriched pocket

Filling the Tank:

Place plate or plastic on substrate
Pour water onto plate to prevent disturbance
Fill slowly to halfway
Plant while easier access
Fill to final level

Maintenance by Substrate Type

Gravel Maintenance

Weekly:

Gravel vacuum 25-30% of substrate during water change
Work in sections (don’t do all at once)
Remove uneaten food and waste

Monthly:

Deep clean one section thoroughly
Rinse filter media
Check for compacted areas

Annually:

Consider adding root tabs near heavy root-feeders
Replace filter media gradually
Stir deep gravel gently to prevent dead zones

Sand Maintenance

Weekly:

Hover siphon just above sand surface
Suck up visible debris sitting on top
DO NOT plunge deep into sand

Monthly:

Gently stir surface sand with fingers or tool
Release any trapped gas bubbles
Remove any debris pockets

As Needed:

Skim surface with net to remove debris
Siphon out uneaten food immediately
Clean filter more frequently (sand can clog)

Warning Signs:

Black spots = anaerobic pockets (stir gently)
Foul odor = hydrogen sulfide (increase stirring)
Compaction = stir surface weekly

Aquasoil Maintenance

Weekly:

Gentle surface vacuum only
Don’t disturb deep layers
Remove visible debris with net or gentle siphon

Monthly:

Dose liquid fertilizers (aquasoil depletes over time)
Add root tabs near heavy feeders after 6-12 months
Trim plants and remove dead leaves

Annually:

Aquasoil nutrients deplete after 1-2 years
Add new root tabs throughout
Consider partial aquasoil refresh if plant growth declines

Never:

Deep vacuum aquasoil (removes nutrients and clouds water)
Stir or disturb layers unnecessarily
Use tap water on disturbed aquasoil (kills bacteria)

Common Substrate Problems

Cloudy Water

Cause: Disturbed sand or aquasoil during filling Solution:

Let settle 24-48 hours with filter running
Add fine filter floss to filter
Water changes if persistent
Prevention: Fill very slowly over plate/plastic

Algae on Substrate

Cause: Excess nutrients, too much light Solution:

Reduce photoperiod by 2 hours
Add fast-growing plants
Manual removal with siphon
Consider algae-eating crew (shrimp, snails, ottos)

Gas Bubbles in Sand

Cause: Organic matter decomposing, anaerobic pockets Solution:

Gently stir surface weekly
Don’t make sand bed too deep (>3 inches risky)
Add Malaysian Trumpet Snails (naturally aerate)

Note: Small bubbles normal; large, frequent bubbles concerning

Plants Not Rooting

Cause: Substrate too coarse or compacted Solution:

Add root tabs near plant bases
Use planting tweezers to make holes
Create pockets with finer substrate
Consider rhizome plants instead (Anubias, Java Fern)

Substrate Shifting

Cause: Strong filter flow, digging fish Solution:

Baffle filter output
Use heavier substrate
Add rocks/wood to hold substrate in place
Create substrate barriers with rocks

pH Issues

High pH:

Cause: Limestone, coral, certain rocks in substrate
Solution: Remove buffering substrate, use inert materials

Low pH:

Cause: Peat, aquasoil, decaying organic matter
Solution: Accept if suitable for fish, or switch substrate

Cost Comparison

Budget Options ($):

Pool filter sand: $0.10 per lb
Play sand: $0.15 per lb
Black Diamond blasting sand: $0.20 per lb
Regular gravel: $0.50 per lb

Mid-Range Options ($$):

CaribSea gravel/sand: $1-2 per lb
Fluval Stratum: $3-4 per lb
CaribSea Eco-Complete: $1-2 per lb

Premium Options ($$$):

ADA Amazonia: $4-6 per lb
UNS Controsoil: $3-5 per lb
Specialty aquasoils: $4-8 per lb

Value for Money:

Best budget: Pool filter sand
Best mid-range: Fluval Stratum
Best premium: ADA Amazonia (for serious aquascapers)

Conclusion

Substrate selection dramatically impacts your aquarium’s success. Match your choice to your goals: sand for bottom-dwelling fish, aquasoil for demanding plants, gravel for easy maintenance.

Remember that substrate lasts years—invest appropriately for your long-term goals. A $50 bag of aquasoil seems expensive but provides years of plant support. Budget sand works perfectly for fish-focused tanks.

Most importantly, once substrate is in place and the tank established, changing it becomes a major undertaking. Research, plan, and choose wisely from the start.

Ready to add hardscape to your substrate? Explore our aquarium hardscape ideas for stunning rock and wood combinations.