Protect the fish and operating level first, then narrow down where water is leaving. Evaporation, splash, overflow, plumbing, and liner problems can look similar. Do not let the pond drain until it stops just to find a leak height.
Record Loss and Changes
Mark a safe reference and record time, weather, rain, refill, and settings. Inspect wet ground, fittings, waste valves, chambers, waterfall edges, and liner margins. Blocked returns or shifted stones can send water outside the lining without a main-pond hole.
Check Water Features
Look for splash, wind-blown water, low edges, roots or material carrying water over the liner, and overflow. Check for waste valves left open. Observe safely without moving load-bearing rocks or walking on unsupported edges.
Compare Circuits with Life Support Protected
If the design permits, isolate one suspected feature using proper valves and instructions. Maintain appropriate aeration, circulation, and biological support by another route. A shutdown comparison may distinguish pumped circuits from the shell, but does not prove a leak location or justify unattended testing.
Control Refilling
Repeated top-ups can hide a leak and expose fish to unsuitable water. Condition new water, record volume, and supervise. Rapid loss, electrical hazards, unstable banks, or levels threatening fish require prompt professional help. Use safe refilling and backup support.
Repair the Identified Material
Identify liner, fitting, joint, or structural defect first. Follow compatible repair instructions for cleaning, drying, priming, cure, and fish contact. EPDM, PVC, and concrete do not share a universal adhesive. Avoid household sealant, random dyes, or generic underwater patch recipes.
Test the Repair
Restore operation and monitor levels under comparable conditions. Keep suspect edges visible until the result is established. Review equipment service, waterfall containment, and routine checks. Persistent or inaccessible leaks need a qualified contractor.