14 · Troubleshooting
When something looks wrong, diagnose the cause before treating the symptom. Most issues trace back to nutrients, oxygen, or balance.
| Symptom | Likely cause | Fix |
|---|---|---|
| Green water (suspended algae) | Excess nutrients + light; new pond cycling | Add plants, cut feeding, increase flow; UV only as last resort |
| String algae (blanket weed) | High nitrate/phosphate, low competition | More oxygenators & marginals, barley straw, manual pull |
| Murky / tea-colored | Tannins from leaves, or suspended clay | Remove leaves, add activated carbon or more plants |
| Foul rotten-egg smell | Anaerobic sludge / no oxygen | Increase circulation, vacuum bottom, add bacteria |
| Fish gasping at surface | Low oxygen (hot, still, overstocked) | Add aeration/fountain immediately, reduce stocking |
| Cloudy after rain | Runoff nutrients washing in | Divert runoff, add more filtration planting |
| Leak (dropping level) | Liner puncture or overflow | Check edges first, then use leak-finder dye |
Barley straw method
A time-honored, chemical-free algae suppressor: place barley straw in a mesh bag in the water (roughly 50 g per m²). As it breaks down it releases peroxides that inhibit algae. It works slowly and is preventative, not a cure.
Avoid
Never use household "algaecides" or bleach. They kill beneficial bacteria and crash the cycle, often making algae worse within days. A natural pond is fixed with biology, not poison.
Diagnosis procedure
- Test the water first — 90% of problems are water-quality related.
- Check the filter — is it running? Is the pump clogged?
- Observe fish behaviour — gasping at surface = low oxygen. Rubbing against objects = parasites. Clamped fins = stress or disease.
- Check recent changes — new fish? Heavy rain? New plants? Temperature swing?
Do not panic-treat
Adding medication without confirming the problem kills beneficial bacteria and may make things worse. Test, observe, research, then treat.
Emergency oxygen boost
If fish are gasping: 1) Add an airstone or position a fountain to break the surface. 2) Pour in dechlorinated water from a tap to add oxygen. 3) Remove any decaying matter. 4) Do not feed until the crisis passes.