# Aquatic Decor & Substrate

Aquatic decor and substrate aren't just a tank's looks: the material underfoot and underhand quietly sets water chemistry. Reactive rock and aragonite raise hardness and pH; active soils and driftwood tannins lower them; inert gravel and resin hold steady. Water type and decor type decide which materials are safe and which plants or fish the setup can support.

## How it works

Everything placed inside a tank sits in constant contact with the water, so its material does chemical work whether or not the buyer wants it to. Calcium-carbonate rock and substrate (aragonite, crushed coral, limestone, seiryu stone) slowly dissolve in slightly acidic water, releasing calcium and raising hardness and pH — wanted in marine reef and African cichlid tanks, unwanted in soft-water planted or blackwater setups. Driftwood and botanicals release tannins that acidify and darken water, the opposite effect. Inert materials — most gravel, resin ornaments, aquarium-safe plastic, porous clay substrates like Flourite — do neither; they just provide surface area and, in planted-substrate products, exchange nutrients from fish waste to roots. Live plants additionally pull nutrients and CO2 from the water column as they grow; artificial plants only occupy space and give fish cover.

## How an expert narrows the choice

```mermaid
timeline
  section 1 · Freshwater, marine, or brackish
    marine_reef : skip Care difficulty, Light and CO2 demand, How it's placed
  section 2 · Substrate, hardscape, ornament, plant, or background
    substrate : ask Substrate material : skip Hardscape material, Reacts with water, or inert, Ready to use, or needs prep, Piece size, Porosity / surface area, Ornament material, Live or artificial plant, Care difficulty, Light and CO2 demand, How it's placed, Background style
    hardscape : ask Hardscape material : skip Substrate material, Grain size, Effect on water chemistry, Substrate color, Ornament material, Live or artificial plant, Care difficulty, Light and CO2 demand, How it's placed, Background style
    ornament : ask Ornament material : skip Substrate material, Grain size, Effect on water chemistry, Substrate color, Hardscape material, Reacts with water, or inert, Ready to use, or needs prep, Piece size, Porosity / surface area, Live or artificial plant, Care difficulty, Light and CO2 demand, How it's placed, Background style, Aquascaping style marketed
    plant : ask Live or artificial plant : skip Substrate material, Grain size, Effect on water chemistry, Substrate color, Hardscape material, Reacts with water, or inert, Ready to use, or needs prep, Piece size, Porosity / surface area, Ornament material, Background style
    background : ask Background style : skip Substrate material, Grain size, Effect on water chemistry, Substrate color, Hardscape material, Reacts with water, or inert, Ready to use, or needs prep, Piece size, Porosity / surface area, Ornament material, Live or artificial plant, Care difficulty, Light and CO2 demand, How it's placed, Aquascaping style marketed
  section 3 · Live or artificial plant
    live : ask Care difficulty, Light and CO2 demand, How it's placed
    artificial_silk / artificial_plastic : skip Care difficulty, Light and CO2 demand, How it's placed, Aquascaping style marketed
```

1. **Freshwater, marine, or brackish.** Freshwater, marine reef, or brackish tank?
   Water type decides which hardscape and substrate materials are appropriate: marine/cichlid setups want calcium-reactive rock and aragonite for hardness, while soft-water freshwater and blackwater tanks need to avoid exactly those materials.
   If marine_reef: skip Care difficulty, Light and CO2 demand, How it's placed.
   Skip if already known: a query that already names 'marine', 'reef', 'saltwater', or 'brackish', an earlier answer naming freshwater fish or plants.

2. **Substrate, hardscape, ornament, plant, or background.** Substrate, hardscape, an ornament, a plant, or a background?
   Each decor type is judged on an unrelated spec — substrate chemistry, rock reactivity, ornament material, plant light/CO2, background mounting — so this fork decides which facet set to ask about next.
   If substrate: ask Substrate material; skip Hardscape material, Reacts with water, or inert, Ready to use, or needs prep, Piece size, Porosity / surface area, Ornament material, Live or artificial plant, Care difficulty, Light and CO2 demand, How it's placed, Background style.
   If hardscape: ask Hardscape material; skip Substrate material, Grain size, Effect on water chemistry, Substrate color, Ornament material, Live or artificial plant, Care difficulty, Light and CO2 demand, How it's placed, Background style.
   If ornament: ask Ornament material; skip Substrate material, Grain size, Effect on water chemistry, Substrate color, Hardscape material, Reacts with water, or inert, Ready to use, or needs prep, Piece size, Porosity / surface area, Live or artificial plant, Care difficulty, Light and CO2 demand, How it's placed, Background style, Aquascaping style marketed.
   If plant: ask Live or artificial plant; skip Substrate material, Grain size, Effect on water chemistry, Substrate color, Hardscape material, Reacts with water, or inert, Ready to use, or needs prep, Piece size, Porosity / surface area, Ornament material, Background style.
   If background: ask Background style; skip Substrate material, Grain size, Effect on water chemistry, Substrate color, Hardscape material, Reacts with water, or inert, Ready to use, or needs prep, Piece size, Porosity / surface area, Ornament material, Live or artificial plant, Care difficulty, Light and CO2 demand, How it's placed, Aquascaping style marketed.
   Skip if already known: a query that already names gravel, sand, soil, rock, driftwood, an ornament, a plant, or a background.

3. **Live or artificial plant.** A live plant, or artificial silk/plastic?
   Live plants need light, CO2, and a placement method matched to the species or they melt; artificial plants need none of that, so this fork decides whether care facets apply at all.
   If live: ask Care difficulty, Light and CO2 demand, How it's placed.
   If artificial_silk or artificial_plastic: skip Care difficulty, Light and CO2 demand, How it's placed, Aquascaping style marketed.
   Skip if already known: a query that already names 'live plant' or 'silk/plastic plant', an earlier answer naming CO2 injection or a light schedule.

## What to surface

### Freshwater, marine, or brackish

Whether the tank holds freshwater, marine/reef (saltwater), or brackish (mixed) water. Water type decides which decor materials are even appropriate: marine reef tanks want calcium-carbonate rock and aragonite sand that buffer pH up, while freshwater planted or soft-water tanks avoid exactly those materials because they raise hardness and stall soft-water fish and plants. [9] [8]

Values: freshwater, marine_reef, brackish.
Question to ask: Freshwater, marine reef, or brackish tank?

Used as: top-level split, filter. Data: derived from listing fields, backfill cost low. Look for it as: Usually stated in the title or category breadcrumb ('Marine', 'Reef', 'Freshwater', 'Brackish').
Keyword match the title/category; CaribSea's own catalog already separates freshwater and marine product lines by name.

### Substrate, hardscape, ornament, plant, or background

Which kind of decor item this is: loose substrate, natural hardscape (rock/driftwood), a molded ornament, an aquarium plant, or a background. Each type is judged on a different spec — a substrate's grain and chemistry, a rock's reactivity, an ornament's material, a plant's light and CO2 needs, a background's mounting — so asking this first avoids asking about CO2 demand on a rock or grain size on a background. [8] [9]

Values: substrate, hardscape, ornament, plant, background.
Question to ask: Substrate, hardscape, an ornament, a plant, or a background?

Used as: top-level split, filter. Data: derived from listing fields, backfill cost low. Look for it as: Derive from the product title and category breadcrumb (gravel/sand vs rock/driftwood vs ornament vs plant vs background).
Title keyword match covers nearly all listings; Fluval and CaribSea's own site navigation uses these same buckets.

### Live or artificial plant

Whether the plant is a living organism that grows and needs light/CO2/nutrients, or an artificial silk or plastic replica that needs none of that. Live plants pull nitrate and CO2 from the water and need matched light, substrate, and sometimes added CO2 to survive; artificial plants need none of that upkeep. Among artificial options, keepers of long-finned fish like bettas often prefer silk over rigid plastic, marketed as gentler on fins. [1] [8]

Values: live, artificial_silk, artificial_plastic.
Question to ask: A live plant, or artificial silk/plastic?

Used as: top-level split, filter. Data: on the listing, backfill cost low. Look for it as: Usually explicit in the title ('Live Anubias', 'Silk Plant', 'Plastic Plant').
Title keyword match; near-universal since live and artificial plants sit in separate catalog sections.

### Effect on water chemistry

Whether the substrate actively changes pH/hardness (active soil lowers it, aragonite raises it) or stays chemically inert. This is the fact that is rarely on the box but decides tank success: an inert substrate under African cichlids, or a reactive aragonite bed under soft-water tetras, will both fight the keeper's target water parameters indefinitely instead of settling. [3] [4]

Values: lowers_pH_softens, neutral_inert, raises_pH_hardens.

Used as: shown on the card. Data: derived from listing fields, backfill cost low. Look for it as: Not a listed field; derive from substrate_material (active soil lowers, aragonite/crushed coral raises, gravel/clay/sand stay neutral).
Pure lookup from substrate_material; no extra research needed per item.
Chart: position on the same water-chemistry axis as substrate_material.

### Reacts with water, or inert

Whether the piece slowly dissolves or leaches into the water (raising hardness for calcium stone, releasing tannins for driftwood) or stays chemically inert. A reactive piece keeps nudging water hardness or pH for as long as it is in the tank, which can quietly stress fish and plants chosen for the opposite conditions months after setup, long after the buyer stopped checking. [2] [1]

Values: reactive, inert, leaches_tannins.

Used as: shown on the card. Data: derived from listing fields, backfill cost low. Look for it as: Not listed; derive from hardscape_material.
Lookup from hardscape_material: reactive_calcium_stone maps to reactive, natural_driftwood maps to leaches_tannins, the rest map to inert.

### Care difficulty

A live plant's ease of care, usually rated easy, medium, or advanced, based on its light, CO2, and nutrient demand. A buyer new to planted tanks who starts with an 'advanced' plant under basic light and no CO2 injection usually watches it melt within weeks; the easy/medium/advanced label is the fastest filter against that outcome. [10]

Values: easy, medium, advanced.
Question to ask: Easy, medium, or advanced care plants?

Used as: filter. Data: on the listing, backfill cost low. Look for it as: Often on the label/listing via Tropica's or the retailer's own Easy/Medium/Advanced (or Easy/Medium/Hard) rating.
Most live-plant retailers already publish a 3-tier difficulty rating; copy it directly rather than re-deriving per species.
Chart: position on a care-difficulty axis, easy to advanced.

### Substrate material

What the loose bottom layer is made of: inert gravel/clay, nutrient-rich active soil, plain sand, aragonite/crushed coral, or none (bare bottom). Active soils lower pH and soften water for heavy root feeders and shrimp but break down within 1-2 years; inert gravel and clay substrates hold nutrients via cation exchange without changing water chemistry; aragonite/crushed coral is for marine or African cichlid tanks that want hardness, not soft-water planted tanks. [3] [4] [8]

Values: inert_gravel_or_clay, nutrient_rich_active_soil, sand, aragonite_or_crushed_coral, bare_bottom.
Question to ask: Plain gravel, active plant soil, sand, or bare bottom?

Used as: filter, shown on the card. Data: on the listing, backfill cost low. Look for it as: Usually named in the title ('Eco-Complete', 'Aqua Soil', 'Play Sand', 'Aragonite Reef Sand').
Title/brand keyword match against known product lines (Flourite, Eco-Complete, Stratum, ADA Aqua Soil map to inert or active by brand).
Chart: position on a water-chemistry axis from acidifying/softening (active soil) through neutral (inert) to hardening (aragonite).

### Hardscape material

What a rock or wood piece is made of: reactive calcium stone (seiryu/limestone), inert stone (lace rock, slate, quartz), real driftwood, or a resin replica. Reactive stone and real driftwood both change water chemistry, in opposite directions; inert stone and resin replicas don't. Buyers assembling a soft-water planted or blackwater tank need to avoid reactive stone specifically, not just 'rock' in general. [2] [8] [9]

Values: reactive_calcium_stone, inert_stone, natural_driftwood, resin_replica.
Question to ask: Real rock, driftwood, or a resin replica?

Used as: filter, shown on the card. Data: on the listing, backfill cost low. Look for it as: Named material in the title (Seiryu, Dragon Stone, Lace Rock, Malaysian/Mopani/Spider driftwood, 'resin' or 'polyresin').
Title keyword match against known trade names; default unnamed 'rock' to inert_stone and unnamed 'wood-look' decor to resin_replica.
Chart: position on the water-chemistry axis, reactive stone hardening through inert to driftwood acidifying.

### Grain size

How fine or coarse the substrate particles are: fine sand/powder, medium gravel, or coarse gravel/stones. Very fine substrate compacts and can trap gas pockets or restrict root penetration; very coarse substrate leaves gaps roots and small fish food fall through. Most planted-tank substrates sit in a fine-to-medium range for exactly this reason. [3]

Values: fine_sand_or_powder, medium_gravel, coarse_gravel_or_stones, mixed_or_unspecified.
Question to ask: Fine sand, medium gravel, or coarse stones?

Used as: filter, shown on the card. Data: needs research, backfill cost medium. Look for it as: Sometimes stated as a grade in the title or bullet points; otherwise inferable from product photos.
Not always on the listing; default to medium_gravel when unstated, since it is the most common retail grade.
Chart: position on a particle-size axis, fine to coarse.

### Substrate color

The visible color of the substrate, from dark black/brown through natural tan to white or brightly colored. Dark substrate is the common choice for making fish colors pop and hiding waste between cleanings; light or white substrate shows detritus more but gets chosen for a specific look, like bright reef sand. [4] [6]

Values: black, red_or_brown, natural_tan_or_beige, white_or_light, other_bright_color.
Question to ask: What color substrate: black, brown, tan, or white?

Used as: filter, shown on the card. Data: on the listing, backfill cost low. Look for it as: Usually named directly in the title ('Flourite Black', 'Flourite Red', 'Sunset Gold', 'Moonlight Sand').
Title keyword match against named color/line variants.
Chart: color swatch.

### Piece size

How large a single rock or driftwood piece is, from small accent pieces to large show-stone centerpieces. The same rock shape is sold in several explicit sizes, and tank volume limits how large a centerpiece can go, so buyers sizing an aquascape pick by piece size before color or shape. [5] [6]

Values: small_accent, medium, large_centerpiece.
Question to ask: Small accent piece, medium, or large centerpiece?

Used as: filter, shown on the card. Data: on the listing, backfill cost low. Look for it as: Usually a size variant in the title or options (e.g. 8"/12"/18", 'Small Accent Pieces').
Title/variant keyword match against explicit size options; default to medium when unstated.
Chart: position on a size axis, small to large.

### Ornament material

What a molded decoration (cave, castle, pipe, skull) is made of: resin, ceramic, or plastic. All three are chemically inert in water, so the real choice is durability and weight: ceramic can crack and sinks fast, plastic can float until weighted, and resin is the most common because it is heavy and holds fine detail. [8]

Values: resin, ceramic, plastic, unspecified.
Question to ask: Resin, ceramic, or plastic ornament?

Used as: filter, shown on the card. Data: on the listing, backfill cost low. Look for it as: Usually in the title or a material bullet point.
Title keyword match; default to resin when unstated, since it is the dominant retail material for cast decorations.

### Background style

The type of backdrop mounted behind or inside the tank: a flat vinyl/photo sheet outside the glass, a static-cling poster, or a rigid 3D foam panel fitted inside the tank. A flat, outside-mounted background is cheap and reversible but always looks flat; a 3D foam background fits inside the tank and can be carved and planted on like real hardscape, but takes up tank volume and is effectively permanent once sealed in. [8]

Values: flat_vinyl_or_photo_outside, static_cling_outside, rigid_3d_foam_inside.
Question to ask: A flat backdrop, or a 3D background panel?

Used as: filter. Data: on the listing, backfill cost low. Look for it as: Usually explicit in the title ('3D Background', 'Vinyl Background Poster').
Title keyword match; near-universal.

### Light and CO2 demand

How much light intensity and often supplemental CO2 a live plant needs to grow well, from low (survives dim, uninjected tanks) to high (needs strong light and injected CO2). A high-light, CO2-demanding plant placed under a basic low-output light with no CO2 will stall, discolor, or rot instead of growing; matching this to the tank's actual light and CO2 setup is the biggest driver of live-plant success or failure. [10]

Values: low, medium, high.

Used as: filter, shown on the card. Data: needs research, backfill cost medium. Look for it as: Occasionally stated on specialist plant-retailer listings; general marketplaces rarely carry it.
Cross-reference the species name against a plant retailer's care database; not derivable from the listing title alone.
Chart: position on a light/CO2-demand axis, low to high.

### Ready to use, or needs prep

Whether the piece can go straight into the tank, or needs curing/soaking first, since dry driftwood floats until it waterlogs. Dry driftwood floats for weeks to months until it waterlogs; keepers who skip pre-soaking or boiling end up with a piece bobbing against the tank lid and tea-colored water. Rock or wood sold pre-cured skips that step. [1]

Values: ready_to_use, needs_soak_or_boil_to_sink, needs_cleaning_only.
Question to ask: Ready to use, or does it need soaking?

Used as: filter, shown on the card. Data: needs research, backfill cost medium. Look for it as: Sometimes stated ('pre-soaked', 'sinks immediately'); otherwise assume real driftwood needs soaking and resin/pre-cured rock does not.
Default natural_driftwood material to needs_soak_or_boil_to_sink and resin_replica/inert_stone to ready_to_use when unstated.

### Aquascaping style marketed

Whether the decor (hardscape set, plant pack, or substrate) is marketed toward a named aquascaping style: Iwagumi (minimal stone arrangement), Dutch style (dense plant rows), nature/jungle, or biotope-correct (matching one real habitat). An 'Iwagumi set' is sold as a small odd number of stones meant to be arranged as one dominant rock plus satellites, not as generic rock by the pound; buying for a named style means piece count and shape matter more than total weight. [1]

Values: iwagumi, dutch_style, nature_or_jungle, biotope_correct, no_named_style.

Used as: shown on the card. Data: needs research, backfill cost medium. Look for it as: Sometimes named directly in hardscape-kit or plant-pack titles ('Iwagumi Stone Set', 'Dutch Style Plant Pack').
Keyword match the title against the four named styles; default to no_named_style when absent.

### Porosity / surface area

How much internal pore space and surface area a rock has for nitrifying bacteria to colonize, separate from whether it chemically reacts with water. Marine reef keepers rely on rock surface area, not just reactivity, for biological filtration; a highly porous rock seeds beneficial bacteria faster and supports more bioload than a dense piece of the same material. [6] [7]

Values: high_porosity, moderate_porosity, dense_low_porosity.

Used as: filter, shown on the card. Data: needs research, backfill cost medium. Look for it as: Rarely stated numerically; dry/live rock lines marketed as porous base rock default high, dense decorative stone (seiryu, lace rock slabs) defaults low.
Classify by product line: dry/live rock and reef base rock default to high_porosity, dense ornamental stone defaults to dense_low_porosity.
Chart: position on a porosity axis, dense to highly porous.

### How it's placed

How the live plant attaches or grows in the tank: planted in substrate by its roots, tied to hardscape by a rhizome, left floating, or grown as a substrate carpet. Planting a rhizome plant like Anubias with the rhizome buried, instead of tied to wood or rock, is a classic beginner mistake that rots the rhizome; placement method is how the species actually survives, not just styling. [1]

Values: rooted_in_substrate, rhizome_attached_to_hardscape, floating, carpeting.

Used as: filter, shown on the card. Data: needs research, backfill cost medium. Look for it as: Not usually a listing field; inferable from the species/category (carpet plants, floaters, and rhizome plants like Anubias/Bucephalandra are named categories on specialist sites).
Cross-reference the species name against known categories (carpet, floater, rhizome, stem/rooted) rather than a per-listing lookup.

## Numbers worth computing

| Metric | Formula | Why |
|---|---|---|
| Substrate cost per liter (price per liter) | `listed_price / (bag_weight_kg / bulk_density_kg_per_liter)` | Bag weight and bulk density both vary by material: CaribSea's own spec sheets list 54-100 lb/ft3 (about 0.87-1.6 kg/L) across substrate lines, and Seachem's bag-volume spec implies about 1.27 kg/L for Flourite, so price per bag misleads; price per liter of finished substrate bed is what's actually comparable across brands. [6] [4] |

## What you give up

- Calcium-reactive rock and aragonite substrate keep hardness and pH up, which reef and African cichlid keepers want and soft-water planted or blackwater keepers specifically avoid by choosing inert or tannin-releasing materials instead. [2] [9] Board branch: "More hardness buffering, less soft-water stability".
- Active, nutrient-rich soils like ADA Aqua Soil grow heavy root feeders and shrimp-tank plants fastest but compact and deplete within a year or two; inert gravel-based substrates like Flourite or Eco-Complete last the life of the tank but need root tabs for the same plants. [3] [4] Board branch: "More plant growth, shorter substrate life".
- Artificial plants need no light, CO2, or fertilizer and never melt, but they don't compete with algae for nutrients or pull CO2 the way a live plant does; an all-artificial tank relies entirely on filtration and water changes for that work. [1] [10] Board branch: "Less maintenance, no biological filtration benefit".

## Words you will meet

- **Cation exchange capacity (CEC)**. A substrate's ability to hold onto nutrient ions (like those from fish waste or fertilizer) so plant roots can use them later.
- **Active substrate**. A nutrient-rich soil-based substrate that lowers pH and softens water as it breaks down, instead of staying chemically neutral.
- **Aragonite**. A calcium-carbonate sand or gravel that dissolves slightly in water, raising hardness and pH; used in marine and African cichlid tanks.
- **Hardscape**. The rock and driftwood structure of a tank, as opposed to its substrate, plants, or molded ornaments.
- **Tannins**. Organic compounds released by driftwood and leaf litter that tint water brown/yellow and make it slightly more acidic.
- **Blackwater**. A tea-colored, soft, acidic water condition created by driftwood and leaf litter, mimicking some tropical rivers.
- **Iwagumi**. A minimalist Japanese hardscape style built from a small odd number of stones arranged around one dominant rock.
- **Dutch style**. An aquascaping style built from dense rows of different plant species rather than rockwork, like an underwater garden bed.
- **Biotope**. An aquascape built to match the plants, rock, and water conditions of one specific real-world habitat.
- **Rhizome**. A thick horizontal stem some aquarium plants (like Anubias) grow from; it rots if buried and should be tied to hardscape instead.
- **Carpet plant**. A low-growing live plant species that spreads across the substrate to form a lawn-like carpet.
- **Root feeder**. A plant that takes most of its nutrients through its roots from the substrate, rather than from the water column.
- **Curing (driftwood)**. Soaking or boiling dry driftwood until it waterlogs enough to sink and stops releasing most of its tannins.
- **Reactive rock**. Rock that contains calcium carbonate and slowly dissolves in water, raising hardness and pH over time.
- **Porosity**. How much internal pore space a rock has, which affects how much surface area is available for beneficial bacteria.
- **Nitrifying bacteria**. Beneficial bacteria that convert toxic fish waste (ammonia) into less harmful compounds as part of the nitrogen cycle.
- **Bioload**. The total amount of waste-producing life, like fish and corals, that a tank's filtration has to keep up with.

## Where we made a call

- Calcium-carbonate rock such as seiryu stone or limestone gradually raises aquarium hardness and pH rather than staying inert. (confidence medium). Grounded in the general CaCO3-dissolves-in-acid reaction, not in an aquarium-specific measurement; a direct aquarium water-test study corroborating the rate wasn't reachable this run. [2] [3]

## References

1. [Aquascaping](https://en.wikipedia.org/wiki/Aquascaping) (primer). Supports: Defines Iwagumi, Dutch style, Nature aquarium, and jungle-style hardscape and planting conventions; Driftwood, leaf litter, and botanicals release tannins that darken and soften/acidify blackwater tanks; Moss and epiphyte plants are commonly grown attached to driftwood rather than rooted.
2. [Calcium carbonate](https://en.wikipedia.org/wiki/Calcium_carbonate) (primer). Supports: Calcium carbonate reacts with acids, releasing calcium ions, carbon dioxide, and water.
3. [Choosing the Best Substrate for a Planted Tank](https://www.aquariumcoop.com/blogs/aquarium/aquarium-substrate) (specialist review). Supports: Inert substrates like Eco-Complete/Flourite have higher cation exchange capacity and don't change pH or hardness; Nutrient-rich active soils like ADA Aqua Soil lower pH and soften water, but break down over time; African cichlid keepers should avoid nutrient-rich active soils that lower pH and soften water; Extreme grain sizes, very fine or very coarse, hinder plant root establishment.
4. [Seachem Flourite](https://www.seachem.com/flourite.php) (spec sheet). Supports: Flourite is a porous clay gravel that is not chemically coated and will not alter the water's pH; Flourite's own spec page lists Flourite Red, Black, and Dark as separate related products; Each 7 kg Flourite bag occupies about 5,500 cm3, giving roughly 1.27 kg per liter.
5. [Dragon Arches](https://caribsea.com/dragon-arches/) (spec sheet). Supports: Dragon Arches freshwater rock sculpture is sold in three sizes: 8", 12", and 18".
6. [2025 CaribSea Catalog](https://caribsea.com/wp-content/uploads/2025/09/2025-CaribSea-Catalog-new_compressed.pdf) (spec sheet). Supports: Exotica Dragon Stone hardscape ships as a standard size and a separate 'Small Accent Pieces' size variant; Super Naturals substrate ships in many named color variants: Sunset Gold, Crystal River, Moonlight Sand, Zen Garden; Dry/base rock's porosity and void space is described as the basis for marine biological filtration; Per-product spec sheets list average bulk density per material, from about 54 to 100 lb per cubic foot.
7. [Live rock](https://en.wikipedia.org/wiki/Live_rock) (primer). Supports: Live rock has as much or more surface area for bacteria than a trickle filter; Rock porosity varies by region: Fiji rock is often porous, Tonga rock is often dense.
8. [Fluval Stratum Series](https://web.archive.org/web/20220517211433/https://fluvalaquatics.com/us/stratum-series/) (spec sheet). Supports: Stratum is a volcanic soil substrate with nutrients and minerals for live aquatic plants; Brand catalog separates decor into driftwood (natural/polyresin), substrate, ornaments, backgrounds, and decor plants.
9. [CaribSea](https://www.caribsea.com/) (spec sheet). Supports: Brand catalog splits products into Marine Substrates, Marine Rocks, Freshwater Substrates, and Freshwater Rocks.
10. [Make Your Aquarium a Success](https://tropica.com/en/guide/make-your-aquarium-a-success/) (specialist review). Supports: Tropica's patented Easy/Medium/Advanced symbol system is printed on plant-pot labels to guide difficulty-matched buying.