How much turbidity is safe in a fish pond, and how do I fix it?
Turbidity is a proxy for two very different things — suspended clay (mud, silt from runoff) or dense plankton (algae, protozoa). Both cloud the water; only one is helpful. The fix depends entirely on which one you have. This is how to tell the difference and act.
Target Secchi disk visibility of 30–40 cm for shrimp ponds and 25–35 cm for tilapia grow-out. Below 20 cm the bloom is dangerously dense (nighttime DO crash risk). Above 60 cm the pond is under-productive. Diagnose clay vs plankton with a settling test before treating.
Step-by-step
- 1
Read the Secchi disk correctly
Lower a black-and-white 20 cm disk into shaded water until it disappears. Measure the depth. Do this at the same time each day (10:00 AM is standard) and the same spot. Morning and afternoon readings should be within 5 cm.
- 2
Settle-test to separate clay from plankton
Fill a clean glass jar with pond water. Let it sit for 4 hours. Clay settles to the bottom as a distinct brown layer; plankton stays suspended and green. If most turbidity settles = clay problem. If it stays cloudy = bloom problem.
- 3
Fix clay turbidity: gypsum + coagulants
Broadcast 200–500 kg/ha of agricultural gypsum (CaSO₄·2H₂O). Calcium bridges negatively charged clay particles and drops them out. Alum (aluminium sulphate) at 20–30 ppm works faster but crashes pH — dose lime alongside. Fix upstream: bund the pond, plant a filter strip against runoff.
- 4
Fix bloom turbidity: partial exchange + shade
For a Secchi below 20 cm from bloom, do a 15–20% water exchange, dose zeolite (100 kg/ha) to bind ammonia the bloom is feeding on, and reduce feed 20% for 48 hours. Do NOT add algaecide — a bloom crash triggers immediate DO collapse.
- 5
Prevent both
For clay: maintain 60 cm+ freeboard, plant vegetation on approach slopes, avoid heavy tractor traffic near bunds. For bloom: match feed rate to biomass, keep C:N ratio around 12–15:1 (dose molasses if needed), and avoid over-fertilising with urea/DAP.
When to call a technician
- Secchi drops below 15 cm and the settle test shows most turbidity is bloom (mortality risk within 24–48h if bloom crashes).
- Secchi is under 20 cm and pH swings more than 1.0 through the day.
- Clay turbidity persists after 500 kg/ha gypsum — soil chemistry may need a full lab test.
- Water turns milky-white or dark-brown suddenly — this is a bloom die-off in progress.
How CAMARON handles this automatically
CAMARON logs Secchi as a daily field entry. The bloom health score combines Secchi, pH swing, and DO trend to flag ponds that are heading for a crash — usually 3–5 days before the die-off event, when a partial exchange still fixes it cheaply.
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