# Aquariums & Tanks

A tank's material and construction, not its price, decide whether it is scratch-resistant and cheap (glass) or light, impact-resistant, and shapable into curves (acrylic); shape and drilling decide fit for a goal like reef-keeping or aquascaping. Volume then sets the stability, weight, and stand strength the tank actually needs.

## How it works

An aquarium is a sealed, transparent vessel — glass panes bonded with silicone, or acrylic sheet thermoformed or solvent-welded at the seams — holding a fixed volume of water under constant hydrostatic pressure, which is why wall thickness and bracing scale with size instead of being arbitrary. Material sets the core trade-off: glass is heavier and scratch-resistant but can only be bonded flat, while acrylic is lighter and can be curved or molded but scratches more easily and used to yellow before UV-stabilized resin became standard. Some tanks add holes drilled through a pane down to a hidden sump for filtration (reef-ready); most instead rely on in-tank or hang-on filtration.

## How an expert narrows the choice

```mermaid
timeline
  section 1 · Glass or acrylic
    glass : ask Glass edge finish, Glass clarity : skip Acrylic seam method, UV-stabilized resin
    acrylic : ask Acrylic seam method, UV-stabilized resin : skip Glass edge finish
  section 2 · Main setup goal
    reef_saltwater : ask Filtration architecture
    brackish : skip Filtration architecture
    planted_aquascape : ask Glass edge finish, Glass clarity : skip Filtration architecture
    freshwater_community / specialist_or_quarantine : skip Filtration architecture
```

1. **Glass or acrylic.** Glass tank, or acrylic?
   Material decides the entire build: scratch-resistant, flat-bonded seams for glass versus impact-resistant, thermoformed curves for acrylic. Construction detail routes from this.
   If glass: ask Glass edge finish, Glass clarity; skip Acrylic seam method, UV-stabilized resin.
   If acrylic: ask Acrylic seam method, UV-stabilized resin; skip Glass edge finish.
   Skip if already known: a query that already names 'glass' or 'acrylic', an earlier answer naming a tank material.

2. **Main setup goal.** Freshwater, planted, reef, brackish, or quarantine?
   Goal routes most else: reef needs a drilled, corrosion-safe build; brackish needs corrosion-safe parts but not drilling; planted wants clear glass; freshwater/quarantine stay plain.
   If reef_saltwater: ask Filtration architecture.
   If brackish: skip Filtration architecture.
   If planted_aquascape: ask Glass edge finish, Glass clarity; skip Filtration architecture.
   If freshwater_community or specialist_or_quarantine: skip Filtration architecture.
   Skip if already known: an earlier answer naming freshwater, planted, reef, saltwater, brackish, or quarantine.

## What to surface

### Glass or acrylic

Whether the tank's walls are glass panes or cast/extruded acrylic sheet. Glass is heavier, cheaper, and far more scratch-resistant, but brittle and only bondable into flat panes, so large or curved shapes get expensive. Acrylic is lighter, stronger against impact, and can be thermoformed into bowfronts, hexagons, or cylinders, but scratches more easily and used to yellow before UV-stabilized resin became standard. [1] [2]

Values: glass, acrylic.
Question to ask: Glass tank, or acrylic?

Used as: top-level split, filter. Data: on the listing, backfill cost low. Look for it as: Almost always stated in the title or material spec ('Glass Aquarium', 'Acrylic Aquarium').
Title keyword match; default to glass when unstated since it is the more common material below large/custom sizes.

### Main setup goal

What kind of system the tank is being set up as: everyday freshwater fish, a planted aquascape, a saltwater reef, a brackish estuarine mix, or a specialist/quarantine tank. Goal decides almost everything downstream: reef setups need hardware that will not corrode in salt and usually a drilled, sump-fed (or integrated AIO) tank; brackish needs the same corrosion-safe hardware but not drilling; planted aquascapes favor rimless, high-clarity glass; freshwater community and quarantine tanks can use the plainest build since neither salt nor display aesthetics drive the purchase. [1] [2] [3]

Values: freshwater_community, planted_aquascape, reef_saltwater, brackish, specialist_or_quarantine.
Question to ask: Freshwater, planted, reef, brackish, or quarantine?

Used as: top-level split, filter. Data: needs research, backfill cost medium. Look for it as: Usually implied by the product category or title ('Reef-Ready', 'Planted Aquarium Kit') rather than a stated field.
Keyword-match title/category; default undecorated glass rectangles to freshwater_community.

### Water volume

The tank's water volume, in litres (and US gallons). Volume sets the physics of everything else: more water buffers temperature and chemistry swings but multiplies weight, footprint, and the stand strength needed, which is why tanks are sold in standard size steps rather than built to arbitrary dimensions. [1] [2]

Range: 10 to 1000 L. Glass construction is standard up to about 1,000 L (260 US gal); nano setups sit under about 75 L, and large showpiece or reef systems run into the hundreds of litres.
Question to ask: About how many litres or gallons?

Used as: filter, sortable. Data: on the listing, backfill cost low. Look for it as: Standard spec on every listing, usually given in both litres and gallons.
Almost universally stated; compute litres from gallons (x3.785) when only one unit is given.
Chart: position on a volume scale, pico to showpiece.

### Size band

A coarse size band aquarists use instead of raw litres: pico, nano, standard, or large/showpiece. Small volumes are far less forgiving: a pico or nano tank swings in temperature and water chemistry much faster than a standard tank, so a mistake a standard tank shrugs off can crash a nano overnight. [1] [2]

Values: pico, nano, standard, large_showpiece.

Used as: shown on the card, filter. Data: derived from listing fields, backfill cost low. Look for it as: Derive from capacity_volume: roughly <=10 L pico (single-sourced, wiki_reef_aquarium), <=75 L (~20 US gal) nano for general tanks (wikipedia_aquarium) — reef-specific 'nano reef' listings use a higher cutoff, up to ~140 L (wiki_reef_aquarium); up to a few hundred litres standard, beyond that large/showpiece.
Pure arithmetic on the stated volume, using the sourced 75 L/10 L cutoffs above, not an invented round number.
Chart: position on the same volume scale as capacity_volume, with stability-risk shading.

### Kit or bare tank

Whether the tank ships bundled with a stand, light, filter, and sometimes a heater as a complete kit, or as a bare tank the buyer equips separately. Kits are convenient and usually cheaper than buying the pieces separately, but the bundled filter, light, and heater are entry-level and often the first things an experienced keeper upgrades; a bare tank costs more up front but lets the buyer match equipment to the actual goal from day one. [2]

Values: all_in_one_kit, bare_tank_only.
Question to ask: An all-in-one kit, or a bare tank?

Used as: filter. Data: on the listing, backfill cost low. Look for it as: Kits are explicitly marketed as 'kit' or 'complete set' and list included equipment; bare tanks list only the tank.
Title keyword match on 'kit' or 'complete'.

### Filtration architecture

Whether the tank has holes pre-drilled in a pane to plumb into a below-tank sump, an integrated rear-chamber ('AIO') build with filtration and overflow built into the tank, or a standard tank with neither. A drilled tank plumbs into a below-tank sump so filtration and dosing gear live out of sight, standard for serious reef setups; an AIO tank builds that same hidden filtration into a rear chamber with no separate sump; a standard tank has neither and needs in-tank or hang-on filtration, and drilling one afterward risks cracking it. [2] [5]

Values: drilled_external_sump, integrated_aio_filtration, standard_undrilled.

Used as: filter, shown on the card. Data: needs research, backfill cost low. Look for it as: Stated as 'reef ready'/'drilled' or 'AIO'/'all-in-one' on the reef/marine subset of listings; reliably stated only there, not on plain freshwater listings, so silence there is a weak signal for standard_undrilled.
Keyword match 'reef ready'/'drilled' -> drilled_external_sump; 'AIO'/'all-in-one' -> integrated_aio_filtration; otherwise default standard_undrilled, with lower confidence outside reef/marine listings.

### Matched stand included

Whether the tank is sold with a stand/cabinet rated for its filled weight, or as a bare tank the buyer must pair with a stand separately. A filled tank weighs roughly its water volume in kilograms plus substrate and rock, far more than ordinary furniture is built to hold, so a stand must be rated for that load and dead level; pairing a bare tank with unrated furniture is a common and dangerous mistake. [1]

Values: sold_with_matched_stand, tank_only.
Question to ask: Need a matching stand, or already have one?

Used as: filter. Data: on the listing, backfill cost low. Look for it as: Kits and furniture-style combos say 'with stand' in the title; bare tanks list without one.
Title keyword match for 'stand' or 'cabinet'; default to tank_only when absent.

### Top cover

What covers the top of the tank: nothing, a flat glass lid held by clips, or a hinged canopy that also houses the light fixture. A canopy hides the light and wiring and cuts evaporation, a clip-on glass lid is the cheap default that still slows evaporation and keeps jumping fish in, and an open top is standard for planted or reef tanks where equipment needs to hang over the rim. [1] [2]

Values: open_top, glass_clip_lid, hinged_canopy.
Question to ask: Open top, glass lid, or a hooded canopy?

Used as: shown on the card. Data: on the listing, backfill cost low. Look for it as: Kits usually state 'with canopy' or 'with glass top'; bare tanks are typically open_top.
Title keyword match for 'canopy', 'hood', or 'glass top/lid'; default to open_top for bare tanks.

### Tank shape

The tank's footprint and silhouette: a plain rectangular box, a bowfront with a curved front pane, a hexagon, an L-shaped corner tank, a cylinder (including the specialist kreisel), or a cube. Shape trades viewing angle and floor-plan fit against buildability: curved and cylindrical shapes need acrylic or laminated glass to form, a corner tank fits a room corner at the cost of front-on viewing area, and a kreisel's circular flow is a specialist shape built to keep delicate, weak-swimming animals like jellyfish off the glass. [1]

Values: rectangular_cuboid, bowfront, hexagon, corner_lshaped, cylinder_or_kreisel, cube.
Question to ask: Rectangle, bowfront, hexagon, corner, or cylinder?

Used as: filter, shown on the card. Data: on the listing, backfill cost low. Look for it as: Always stated in the title or product type.
Title keyword match; default to rectangular_cuboid when unstated, by far the most common shape.

### Glass clarity

Whether a glass tank uses standard float glass (a faint green cast) or low-iron 'ultra-clear' glass with that tint removed. Standard float glass has a faint green cast that's barely visible alone but shows at the edges of a large tank; low-iron glass removes it for a truer view, at a price premium, and unlike acrylic its clarity does not fade over the tank's life. [5] [6]

Values: standard_float_glass, low_iron_ultra_clear.
Question to ask: Standard glass, or low-iron ultra-clear?

Used as: shown on the card, filter. Data: on the listing, backfill cost low. Look for it as: Stated as 'ultra-clear', 'low-iron', or a named clarity line ('CLEAR' series) in the title/description; silent usually means standard float glass.
Keyword match 'ultra-clear'/'low-iron'; default to standard_float_glass otherwise. Only applies when tank_material is glass.

### Footprint (L x W x H)

The tank's external length, width, and height, typically given in inches or centimetres alongside the volume. Two tanks of the same litres can have very different footprints and heights, so the stated length, width, and height decide whether a tank fits a room, a stand, or a shelf, independent of the volume number. [5]

Question to ask: What floor space and height do you have?

Used as: shown on the card, filter. Data: on the listing, backfill cost low. Look for it as: Standard spec row on virtually every listing, given as length x width x height in inches or cm, alongside the volume.
Parse the stated L x W x H string directly; rarely needs lookup.

### Glass edge finish

How a glass tank's panes are finished at the edges: modern silicone-sealed with plastic trim top and bottom, rimless with no trim at all, or an older metal-framed build. Trim-free rimless tanks show an uninterrupted view and are preferred for aquascaping, but expose sharp glass edges and rely entirely on the silicone seam for strength. Framed tanks are effectively obsolete now that silicone sealant is strong enough to hold panes without a structural frame. [1]

Values: trimmed_frameless, rimless_trimfree, framed_vintage.

Used as: shown on the card, filter. Data: needs research, backfill cost low. Look for it as: Title or description usually says 'rimless' when it applies; otherwise assume standard trimmed construction.
Keyword match on 'rimless'; metal-framed tanks are rare enough to default away from.

### UV-stabilized resin

Whether the acrylic resin is UV-stabilized, which keeps it from yellowing under long-term light exposure. Before UV stabilization became standard, acrylic tanks discolored over years under aquarium lighting; it is now the default, but older stock or bargain tanks may not specify it, which matters for a tank expected to last decades. [1]

Values: uv_stabilized, unspecified.

Used as: shown on the card. Data: needs research, backfill cost low. Look for it as: Premium acrylic brands state 'UV-stabilized' in the material spec; budget listings often omit it.
Default to uv_stabilized for current-production tanks from established brands; mark unspecified otherwise.

### Acrylic seam method

Whether an acrylic tank is heat-bent/molded into a shape with few or no seams, or built from flat acrylic panels fused at the edges with acrylic-soluble cement. Thermoforming is what makes curved fronts, hexagons, and cylinders possible at all; a seamed panel tank is cheaper but has more bonded joints, which are the weak point if a tank is ever going to leak. [1]

Values: seamless_thermoformed, solvent_welded_panels.

Used as: shown on the card. Data: needs research, backfill cost medium. Look for it as: Rarely stated directly; infer from shape (a cylinder or curved front is necessarily thermoformed).
Default to solvent_welded_panels for plain rectangular acrylic tanks, the simpler and more common build.

### Overflow plumbing

How water gets from the display tank down to the sump: through an internal overflow box built into a drilled tank, or an external 'hang-on' box siphoning over the rim of an undrilled tank. Internal overflows are quieter and harder to lose siphon on but take up display space and require a drilled tank; hang-on overflows let any undrilled tank run a sump but add a visible box and depend on a continuous siphon that can break. [2]

Values: internal_overflow_box, external_hangon_overflow.

Used as: shown on the card. Data: needs research, backfill cost medium. Look for it as: Stated for drilled kits; hang-on overflow boxes are usually sold and listed separately from the tank.
Drilled listings default to internal_overflow_box; an undrilled tank needing a sump implies an added external_hangon_overflow.

## Numbers worth computing

| Metric | Formula | Why |
|---|---|---|
| Filled weight | `capacity_volume (L) x 1 kg/L (or x 8.34 lb per US gal), plus substrate/rock, excluding the tank's own glass or acrylic weight` | Water alone weighs about 1 kg per litre (8.34 lb per US gallon), so a 200 L tank holds roughly 200 kg of water before substrate, rock, or the tank itself — which is why a stand needs an explicit weight rating, not just a furniture-grade guess. [1] [4] |

## What you give up

- Glass resists scratches and costs less, but is brittle, heavier, and limited to flat bonded panes; acrylic trades those for impact strength, lighter weight, and thermoformed curves, at the cost of scratching more easily. [1] Board branch: "See more acrylic tanks".
- A reef-ready drilled tank hides filtration in a sump and leaves more room to upgrade equipment, but costs more, and drilling a tank after purchase risks cracking it; an undrilled tank is cheaper and simpler but needs an external hang-on overflow to run a sump. [2] Board branch: "See more reef-ready tanks".

## Words you will meet

- **Rimless**. A tank built with no plastic trim at the top or bottom edge, held together purely by the silicone seam.
- **Sump**. A second tank, usually hidden in the stand, that holds filtration equipment out of sight of the display tank.
- **Overflow box**. The compartment that catches water pouring from the display tank and feeds it down to the sump.
- **Reef-ready**. Industry shorthand for a tank pre-drilled for a sump, aimed at reef and serious freshwater setups.
- **Hang-on overflow**. An external box clipped over the back rim of an undrilled tank that siphons water down to a sump without drilling.
- **UV-stabilized**. Resin treated so it resists yellowing from long-term light exposure, now the default for acrylic tanks.
- **Thermoformed**. Heated until pliable and bent or molded into a shape, rather than cut flat and glued at seams.
- **Solvent-welded**. Acrylic panels joined using a solvent cement that chemically fuses them, rather than an adhesive that just glues the surface.
- **Kreisel**. A specialist cylindrical tank, named from the German for 'spinning top', with circular water flow to keep weak-swimming animals like jellyfish off the glass.
- **Nano tank**. A small tank, roughly under 75 litres (about 20 US gallons) for general fishkeeping, though reef-specific listings use a higher cutoff up to about 140 litres, swinging in temperature and chemistry faster than a standard tank.
- **Pico tank**. An especially small tank, roughly 10 litres (2.5 US gallons) or less, even less forgiving of mistakes than a nano tank.
- **Brackish**. Water with a salinity between fresh and full seawater, roughly 0.5 to 30 parts per thousand, mimicking estuaries where rivers meet the sea.
- **Bowfront**. A tank whose front pane curves outward, giving a wider view than a flat pane of the same width.
- **Canopy**. A hinged, hooded cover that houses the light fixture and hides the wiring above the tank.
- **Quarantine tank**. A separate, usually plain tank used to isolate new or sick fish before adding them to the main display, limiting the spread of disease.
- **Aquascape**. An underwater scene arranged with plants, rock, and wood for visual composition, not just a fish habitat.
- **AIO (all-in-one)**. A tank with filtration, overflow, and return plumbing built into a rear chamber of the tank itself, instead of a separate drilled sump.

## Where we made a call

- The classic 'one inch of fish per gallon' rule is too simplistic; surface area and bioload matter more than raw volume. (confidence medium). Sources disagree. Multiple competing rules exist (per gallon, per surface area, per litre); experienced aquarists note growth rate, activity, and filtration capacity aren't captured by any simple ratio. [1]

## References

1. [Aquarium](https://en.wikipedia.org/wiki/Aquarium) (primer). Supports: Glass tanks are standard to about 1,000 litres (260 US gal) before engineering limits apply; Acrylic is lighter and stronger but scratches more easily than glass; Silicone sealant eliminated the need for a structural metal frame; Water weighs 1 kg per litre (8.345 lb per US gallon); Mini aquariums are under about 150 litres (40 US gallons); nano aquariums are under about 75 litres (20 US gallons); Lists cuboid, hexagonal, corner, and bowfront as standard tank shapes; Kreisel tanks are circular-flow cylinders built to hold jellyfish; Stands must be strong and level or the tank may crack; Classic inch-per-gallon stocking rules are oversimplified per aquarists; States brackish water salt level as 500 to 30,000 PPM (0.5 to 30 ppt).
2. [Reef aquarium](https://en.wikipedia.org/wiki/Reef_aquarium) (primer). Supports: Defines reef-ready/drilled tanks as pre-drilled for sump filtration; Internal overflow boxes vs external hang-on overflows feed the sump; Nano reefs are commonly sold as complete kits with stand and lighting; Pico reef tanks are roughly 10 litres (2.5 gallons) or less; Small tank volumes swing in water chemistry faster than larger tanks; Canopy houses the light fixture above the display tank.
3. [Salinity](https://en.wikipedia.org/wiki/Salinity) (primer). Supports: Confirms brackish water salinity range of roughly 0.5 to 30 ppt.
4. [Water - Density, Specific Weight and Thermal Expansion Coefficient](https://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html) (spec sheet). Supports: Confirms water weighs about 8.34 lb per US gallon near room temperature.
5. [Waterbox Aquariums product catalog](https://waterboxaquariums.com/products.json) (spec sheet). Supports: CLEAR and CLEAR MINI lines market rimless, ultra-clear glass as distinct from standard glass tanks; CLEAR series runs 24 to 72 inches, stated as external size on the listing; AIO series builds filtration, overflow, and return into the tank itself, not a drilled sump.
6. [Acrylic vs Glass Aquariums: Which is Better?](https://fishkeepingworld.com/acrylic-vs-glass-aquarium/) (other). Supports: Lists Clarity as its own comparison heading between glass and acrylic aquarium tanks.