uS/cm
Conductivity
What is it
Electrical conductivity (EC) measures water's ability to carry electrical current, expressed in microsiemens per centimeter (µS/cm).
Pure distilled water does not conduct electricity (0 µS/cm); current is carried only by dissolved ions such as calcium, magnesium, sodium, and nitrate. More ions mean higher conductivity.
TDS and conductivity are close cousins: a TDS meter actually reads conductivity and multiplies it by a factor, often 0.5 or 0.64, to estimate TDS. Conductivity is the scientifically purer measurement because it does not estimate which salt is dissolved.
Why it matters
Conductivity is the professional measurement for ornamental shrimp keeping. Experienced breeders speak in µS rather than TDS to avoid errors from the different conversion factors used by commercial TDS pens.
It is an excellent indicator of cumulative pollution: a significant rise between water changes means substantial accumulation of inorganic fertilizers, including nitrate/phosphate, or contaminants.
Aquatic species can be extremely sensitive to conductivity, even more than pH. In Amazonian blackwater systems, the sharp conductivity drop brought by rain triggers breeding in rare species.
Ideal ranges
Interactions with other parameters
Conductivity is tightly linked to ionic purity. A progressive rise without fertilizer dosing indicates a heavy biological load or mineral-releasing substrates. Each 1 dGH of hardness increases conductivity by about 33 µS/cm.
| Tank type | Min | Max | Unit |
|---|---|---|---|
| Tropical community | 300 | 700 | µS/cm |
| Planted high-tech | 300 | 600 | µS/cm |
| Planted low-tech | 300 | 800 | µS/cm |
| Shrimp tank | 200 | 300 | µS/cm |
Out of range: what happens
Conductivity that is too high impairs soft-water fish's ability to release ammonia and body fluids through their gills, leading to fluid retention and kidney failure. In shrimp, high salinity inhibits egg hatching and moulting.
Conductivity that is too low without adequate buffers removes the water's ability to stabilize pH, exposing livestock to potentially lethal sudden swings, or acid crash.
Rapid changes, as with TDS, cause fatal osmotic shock within minutes or hours. New fish should be drip-acclimated slowly to equalize conductivity.
Common Myths
- Conductivity and TDS are two names for the same thing; they are related, but conductivity measures current while TDS estimates solid weight, and different salts change conductivity differently at equal weight.
- Conductivity measurements do not depend on temperature; they depend greatly on it, so pen testers use internal automatic compensation.
Measurement and adjustment
How to measure
Use an EC meter or a dual-mode TDS meter that reads directly in microsiemens (µS); the sensors are technologically identical.
Conductivity is affected by temperature, rising about 2% for every degree Celsius. Better meters use ATC (Automatic Temperature Compensation) to correct the reading to the 25°C standard.
Gently move the probe in the water to release trapped air bubbles and read the result after it stabilizes, within a few seconds.
How to adjust
To reduce conductivity, make water changes with RO/DI (Reverse Osmosis / De-Ionized) water, which measures 0-10 µS.
To raise it, add a calibrated amount of remineralizing salts, GH+ or GH/KH+, to change water. Never add higher-conductivity water directly to the tank without dissolving the salts separately.
For example, with SaltyShrimp GH+ to reach about GH 6 for Caridina cantonensis, remineralize RO water to conductivity of 200 +/- 50 µS.
Pro Tips
- In Discus breeding tanks requiring very pure water, 50-80 µS/cm, a conductivity meter instantly shows whether RO resins are exhausted or need maintenance as permeate conductivity rises.
- Calibrate the pen tester every 3 months with specific buffer solutions, for example 1413 µS/cm, for professional accuracy.