Stocking &
Compatibility
Most aquarium problems don't come from equipment failure — they come from too many fish, added too quickly, or mixed without understanding behaviour.
What Overstocked Really Means
Overstocking is not just about fish size. A tank can be overstocked even when fish are small, water looks clear, tests appear fine, and filtration is powerful.
Overstocking occurs when waste production exceeds biological processing, fish are stressed by crowding or territory loss, feeding increases faster than stability, or behavioural needs aren't met.
Key PointClear water does not equal a healthy system.
Behaviour Comes Before Size
Compatibility charts often fail because they focus on size, not behaviour. When stocking, always consider activity level, territorial behaviour, social needs (schooling vs solitary), feeding competition, and aggression under stress.
Why Rules of Thumb Fall Short
Rules like "1 inch of fish per gallon" ignore body mass, waste output, behaviour, filtration maturity, and feeding style. Instead, think in terms of bioload, tank footprint (swimming space matters more than height), and stability over time.
Simple RuleIf you're unsure whether to add more fish — the safest answer is usually don't.
Stocking Slowly (This Matters More Than Numbers)
- Add small groups, not full stock lists
- Wait 1–2 weeks between additions
- Observe feeding and behaviour before adding more
Rushing stocking is one of the most common causes of delayed losses.
Beginner Mistakes to Avoid
- Overstocking early "because the tank looks empty"
- Mixing incompatible temperaments
- Adding multiple species at once
- Ignoring adult size and behaviour
- Stocking to filtration capacity instead of stability
- Assuming losses are "normal"
RememberLosses are usually a signal — not bad luck.
Quick Reference
- Behaviour matters more than size
- Add fish slowly, not all at once
- Clear water ≠ stable system
- Crowding causes stress before test failures
- When unsure, don't add more
- Patience here prevents long-term problems
Important Context & Expectations
Stocking outcomes depend on tank size, filtration maturity, feeding practices, species behaviour, and maintenance consistency. Losses caused by overstocking or incompatibility are not product faults.
For full details refer to our Terms & Conditions and Claims, Replacement & Insurance pages.