Tank Dimensions — Why Tall Tanks Are Best for Discus
Discus are tall-bodied fish that grow to 15-20 cm in diameter and require vertical swimming space that standard rectangular tanks do not always provide. The ideal discus tank has a height of at least 50 cm, with 60 cm being optimal. A 120×50×60 cm tank (360 litres) is considered an excellent size for a community of 6-8 discus. The tall profile also creates a larger visual water column that showcases discus body shape far better than a low, wide tank designed for bottom-dwelling fish.
Tank width matters for multiple fish — discus establish gentle dominance hierarchies and need enough lateral space to maintain comfortable distances without constant conflict. A tank narrower than 40 cm will force fish together in ways that create chronic stress. In Cambodia's urban apartments, space constraints are real, but a 90×45×55 cm tank (223 litres) is a workable compromise that fits most living rooms while providing adequate discus housing. Custom glass tanks are common in Phnom Penh and often cheaper than imported standard sizes.
Glass thickness is critical for tall tanks. A 60 cm tall tank with 6 mm glass is dangerously underbuilt — the hydrostatic pressure on the lower panels requires 8 mm minimum glass for tanks of this height, with 10 mm being the safe standard for 300+ litre tanks. Local Phnom Penh glass workshops can build custom discus tanks to your specifications, and it is worth specifying 10 mm glass throughout for peace of mind. Ask to see the silicone bead quality on the joints before purchasing — inadequate silicone is the most common cause of tank failures.
- ✦Specify a minimum 60 cm tank height when ordering custom glass tanks in Phnom Penh — short tanks stress discus and limit colour expression
- ✦Ask your tank builder to install a background brace on tanks wider than 90 cm — prevents glass bowing under water pressure
- ✦Position the tank away from direct sunlight and air conditioning vents — both cause temperature instability that stresses discus
Bare Bottom vs Planted — the Honest Comparison
The bare bottom tank is the standard choice for serious discus keepers and all discus breeders. Without substrate, uneaten food and waste are immediately visible and easily siphoned during water changes. Bare bottom tanks are easier to clean, harbour fewer bacteria in accumulated detritus, and allow you to see exactly how much your discus are eating at each feeding. The aesthetic is clinical but functional, and many keepers add visual interest through carefully placed driftwood and background colour rather than substrate.
Planted discus tanks are beautiful and entirely possible, but require significantly more expertise and equipment. The challenge is that discus prefer warm (28-30°C) soft acidic water that is changed daily — conditions that stress or kill many popular aquarium plants. Plants that survive and thrive in discus tanks include Amazon sword (Echinodorus bleheri), Vallisneria, Anubias (attached to driftwood), Java fern, and some Cryptocoryne species. These plants tolerate warm soft water and can be established with LED lighting in the 30-50 PAR range. CO2 injection is generally not needed for these low-demand species.
The compromise approach popular with Cambodia discus keepers is a "minimal planted" setup: fine sand substrate 2-3 cm deep, 2-3 large Amazon sword plants in corners, driftwood in the centre, and open swimming space dominating the layout. This provides biological filtration from plant roots and substrate bacteria, aesthetic warmth, and far easier maintenance than a full planted tank. For first-time discus keepers, bare bottom is strongly recommended for the first year — master the fish before adding the complexity of plant care.
- ✦If using substrate, limit depth to 2-3 cm maximum — deep substrate traps waste that creates dangerous ammonia pockets in a discus tank
- ✦Anubias and Java fern attached to driftwood never need replanting and tolerate full discus conditions — ideal starter plants
- ✦Use fine silica sand rather than gravel in planted discus tanks — gravel traps waste between particles, sand surface-collects for easier siphoning
Filtration — Canister Filters and Gentle Flow
Discus come from slow-moving blackwater environments and are stressed by strong water currents. Filtration for discus must balance biological capacity (handling the waste load of large, frequently fed fish) with minimal water movement. Canister filters are the gold standard for discus tanks — they provide high biological filtration capacity while allowing you to use spray bars or lily pipes that diffuse the return flow across the water surface without creating current. A canister rated for 3-4× the tank volume per hour is the target specification.
Popular canister filters available in Cambodia through Thai and Singaporean imports include the Eheim Classic and Professional series (German engineering, highly reliable), Oase BioMaster (German, with built-in pre-filter), Sunsun HW series (Chinese, affordable and widely available in Phnom Penh for $25-$60 USD), and Fluval FX series for larger tanks. For a 200-litre discus tank, a canister with 1000 L/hour output provides excellent filtration when fitted with a spray bar that divides the flow across the full tank length.
Filter media loading matters significantly for discus filtration. The first chamber should contain mechanical media (coarse sponge or filter floss) to trap particulate waste. Subsequent chambers should contain biological media — ceramic rings or sintered glass (like Eheim Substrat Pro or Seachem Matrix) that provides massive surface area for nitrifying bacteria. Chemical media (activated carbon) is optional and should be removed after use — it does not belong in a permanently loaded discus filter. Clean mechanical media weekly, biological media every 3-6 months in tank water only, never tap water.
- ✦Install the spray bar return horizontally just below the water surface pointing toward the glass — this ripples the surface for oxygenation without creating directional current
- ✦Run two smaller canisters instead of one large one — if one fails or needs cleaning, the second maintains biological filtration and avoids a crash
- ✦Never clean all filter media at once — stagger cleaning so biological colonies are never completely disrupted
Black Background and Driftwood — Decor That Serves the Fish
A black or dark background on a discus tank is not just aesthetic — it serves a genuine biological purpose. Fish perceive their background as sky or open space, and a transparent or light background makes discus feel exposed and vulnerable. Discus against a black background display their maximum colour intensity because they do not need to darken their bodies as camouflage against a threatening environment. The contrast also prevents discus from attacking their own reflections, which is a common problem with mirror-like glass backgrounds.
Driftwood serves multiple important functions in a discus aquarium. Hardwoods like Malaysian driftwood (also called ironwood or Mopani wood) slowly leach tannins into the water, naturally lowering pH and KH while releasing humic acids that have mild antifungal and antibacterial properties. This natural acidification supports the soft water environment discus need without chemical intervention. Driftwood also provides visual structure that breaks lines of sight, reducing territorial aggression in groups and giving nervous fish somewhere to orient themselves.
In Cambodia, Malaysian driftwood and locally sourced tropical hardwoods are available from aquarium suppliers in Phnom Penh at very affordable prices. Always boil new driftwood for 30-60 minutes before adding to a discus tank — this kills surface bacteria, reduces tannin leaching intensity, and softens the wood. Soak pre-boiled wood in clean water for 1-2 weeks to allow excess tannins to leach out before adding to your tank. The water will turn tea-coloured during soaking — this is normal and the colour will fade within weeks of the wood being in a filtered tank.
- ✦Apply self-adhesive black vinyl film to the outside rear glass panel — far cheaper than aquarium background paper and creates a perfect seamless finish
- ✦Weight new driftwood with stainless steel screws into a slate base until it becomes waterlogged and sinks naturally (2-6 weeks)
- ✦Locally sourced jackfruit wood (ដើមខ្នុរ) can be used after thorough drying and boiling — ask local Cambodian aquarists for their preferred local wood species
Quarantine Tank — Non-Negotiable for Discus Keepers
A quarantine tank is not optional for discus keepers — it is the single most important disease prevention tool available. Every new fish introduced to an established discus colony must spend 3-4 weeks in a separate quarantine tank before joining the main tank. Discus carry diseases (particularly Hexamita and gill flukes) that may be subclinical — the fish look healthy but are infectious. Introduction of a carrier fish into a healthy colony can cause devastating losses that dwarf the cost of a basic quarantine setup.
A quarantine tank for discus needs to be 60-100 litres with a bare bottom, a sponge filter (pre-seeded in your main tank), a quality heater, and a thermometer. No substrate, no decorations beyond one piece of driftwood for the fish to orient against. Basic water change schedule of 50% daily during the quarantine period. The setup costs under $30 USD using a basic glass tank, budget heater, and air-driven sponge filter. This investment protects a main display tank worth potentially 10-20× more.
During quarantine, observe the new fish carefully every day. Healthy discus should be eating within 3-5 days, displaying good colour, and swimming actively. Warning signs include: white stringy feces (internal parasites), rapid gill movement (gill flukes or low oxygen), persistent darkness (stress or infection), refusal to eat after 7 days (Hexamita), or visible spots/patches (ich, bacterial infection). Treat any symptoms in the quarantine tank — never add a sick fish to your main display tank under any circumstances, no matter how tempting the fish may be.
- ✦Keep a sponge filter permanently running in your main tank so you always have a pre-seeded biological filter ready for quarantine use
- ✦Quarantine local fish for 3 weeks minimum, imported fish for 4 weeks minimum — import stress weakens immune systems and masks symptoms
- ✦Photograph new fish daily during quarantine to track subtle colour and fin changes that are hard to notice in real-time observation