300L setup
Complete 300L discus tank setup
The recommended configuration for 6-8 discus: excellent parameter stability and room to grow.
Why 300L is the ideal volume for beginners
A 300L tank (approx. 120×50×50 cm) offers the best balance between space for fish, stability and cost. The larger volume means small mistakes (overfeeding, a late water change) don't lead straight to disaster.
At this volume you can comfortably keep 6–8 adult discus plus compatible tank mates (corydoras, cardinal tetra, surface fish).
Dual filtration recommended
For 300L, the recommendation is a main external filter of 1200-1500 L/h + a backup filter (internal sponge or a second smaller external). If the main filter fails, you have time to act without the tank suffering.
Weekly maintenance
Water changes of 30-40% weekly are the rule. With a 300L tank, that's 90-120L per week — the point where it's worth investing in a semi-automatic water change system (Python or a DIY solution).
✓ What's included
Tick them off as you get them — progress saves automatically on this device.
Progress: 0/90%
Clear steps: from box to your first discus
- 1Check the stand/furniture — a full 300L tank weighs ~370 kg and needs even support.
- 2Level the tank, add substrate (3–5 cm) and arrange the hardscape (driftwood, rocks).
- 3Mount the main external filter + secondary filter (internal sponge) — a mandatory safety bonus.
- 4Install both 150W heaters on opposite walls, set to the same temperature (28–29°C).
- 5Fill with dechlorinated water, start the filters and check for leaks for 24h.
- 6Cycle 4–6 weeks with weekly NO2/NO3 monitoring, until NO2 stays consistently 0.
- 7Gradual introduction: 6–8 discus at once after a 2–3 hour drip acclimation.
Common mistakes to avoid
- A single 300W heater — if it fails ON, it boils the tank; if it fails OFF, all the fish die.
- Undersized filter — for 300L you need at least 1200 L/h effective (not the rated figure).
- No secondary filter — without a backup, any failure becomes a crisis in 24h.
- Water changes under 30% weekly — even at 300L nitrates climb without a routine.
- Stocking one by one — discus get stressed and aggressive hierarchies form; add at least 6 at once.
- Quarantine ignored for fish added later — you risk infecting the existing group.
Frequently asked questions
Why two heaters instead of one large one?
Two smaller heaters are much safer. If one fails stuck ON, the other doesn't compensate alone and you don't boil the tank. If one dies OFF, the other holds the temperature until you step in.
How much does it cost monthly to run a 300L tank?
Roughly 150-250 RON/month: electricity, water, food, conditioners and consumables. Use our monthly cost calculator for an exact estimate.