NH3-100 Ammonia Gas-Sensing Electrode

Overview

The NH3-100 is an advanced gas-sensing electrode specifically designed for measuring dissolved ammonia (NH3) in water. Unlike standard ammonium electrodes, this sensor measures the un-ionized ammonia form, which is particularly toxic to aquatic life. This makes it essential for aquaculture, wastewater treatment, and environmental monitoring.

Key Features

• Gas-Sensing Technology: Measures dissolved ammonia (NH3), not just ammonium ions
• Wide Range: Measures from 0.05 to 1,400 mg/L (ppm)
• Digital Output: RS485 Modbus RTU for seamless integration with SCADA and IoT systems
• Fast Response: Results within 60 seconds
• Automatic Temperature Compensation: Integrated PT1000 sensor for accurate readings
• Direct Connection: Connect directly to computer or PLC without additional instrumentation
• High Protection: IP68 waterproof rating ensures reliable operation

Applications

• Aquaculture and fish farming
• Shrimp farming systems
• Wastewater treatment plants
• Industrial effluent monitoring
• Environmental water testing
• Hydroponic systems
• Biogas production
• Agricultural runoff assessment
• Drinking water source monitoring
• Laboratory analysis

Technical Specifications

The NH3-100 delivers precise dissolved ammonia measurements from 0.05 to 1,400 mg/L with automatic temperature compensation. The gas-sensing membrane selectively detects NH3 molecules that diffuse across the membrane, providing specific measurements of the toxic un-ionized form. Unlike ion-selective electrodes that measure NH4⁺, the gas-sensing design is unaffected by dissolved cations, providing true NH3 readings without chemical interference.

Understanding Ammonia vs. Ammonium

In water, total ammonia nitrogen (TAN) exists in two forms:

• NH3 (Ammonia): Un-ionized form, highly toxic to fish and aquatic organisms
• NH4⁺ (Ammonium): Ionized form, significantly less toxic

The ratio between these forms depends on pH and temperature:

• At pH 7.0, 25°C: ~0.6% exists as toxic NH3
• At pH 8.0, 25°C: ~5.4% exists as toxic NH3
• At pH 9.0, 25°C: ~36% exists as toxic NH3

Higher pH and higher temperature both shift the equilibrium toward the toxic NH3 form. The NH3-100 specifically measures this dangerous fraction, making it critical for aquaculture operations where pH can fluctuate.

Ammonia Toxicity Thresholds in Aquaculture

Understanding NH3 limits is essential for preventing fish kills:

Freshwater Fish:

• Safe: < 0.02 mg/L NH3
• Stress onset: 0.02 - 0.05 mg/L NH3
• Sublethal effects: 0.05 - 0.2 mg/L NH3 (reduced growth, immune suppression)
• Lethal: > 0.2 mg/L NH3 (species-dependent)

Shrimp (Penaeus/Litopenaeus):

• Safe: < 0.1 mg/L NH3
• Chronic stress: 0.1 - 0.5 mg/L NH3
• Acute toxicity: > 1.0 mg/L NH3

Salmonids (trout, salmon):

• Safe: < 0.012 mg/L NH3 (most sensitive species)
• EU regulatory limit: 0.025 mg/L NH3

The NH3-100’s low detection limit of 0.05 mg/L allows early detection before concentrations reach damaging levels.

pH and Temperature Effects on Ammonia Toxicity

The fraction of toxic NH3 increases dramatically with pH and temperature:

pH	15°C	20°C	25°C	30°C
7.0	0.3%	0.4%	0.6%	0.8%
7.5	0.9%	1.2%	1.7%	2.5%
8.0	2.8%	3.8%	5.4%	7.5%
8.5	8.5%	11.2%	15.3%	20.3%
9.0	22.8%	28.4%	36.3%	42.5%

This table shows why continuous NH3 monitoring is essential - a small pH increase can multiply the toxic ammonia concentration several times.

Ammonia Sources in Aquaculture Systems

Common ammonia sources that the NH3-100 helps you track:

• Fish metabolism: Ammonia excreted through gills and urine (primary source)
• Uneaten feed: Decomposing feed releases nitrogen compounds
• Dead organisms: Decaying fish, algae, and organic matter
• Biofilter failure: Nitrifying bacteria disruption in RAS systems
• Overfeeding: Excess protein increases ammonia production
• Overcrowding: Higher biomass density increases ammonia load

Installation and Calibration

The NH3-100 is designed for continuous inline monitoring or portable spot-checking:

Mounting: Submersible with IP68 protection. Install in a representative flow area, avoiding dead zones and air pockets. The sensor should be positioned where water circulates naturally past the gas-sensing membrane.

Calibration: Two-point calibration using standard ammonia solutions. Calibrate at concentrations bracketing your expected range. Recalibrate every 2-4 weeks depending on the application. In high-fouling environments, weekly cleaning and calibration is recommended.

Maintenance: Clean the gas-permeable membrane periodically to prevent biofilm buildup. Inspect the membrane for damage or clogging. Replace the membrane cap according to the maintenance schedule.

Connectivity and Integration

The NH3-100 supports dual output for flexible system integration:

RS485 Modbus RTU:

• Connect to Agrinovo Omni Genesis or Exodus controllers
• Multi-drop bus networking (up to 32 sensors per bus)
• Standard Modbus registers for ammonia concentration and temperature
• Compatible with SCADA, PLC, and IoT gateway systems

RS485 Modbus RTU Output:

• Direct connection to traditional controllers and data loggers
• Scalable output range mapped to measurement range
• Loop-powered or externally powered configurations

IoT Integration:

• Pair with Omni Genesis/Exodus for cloud-based ammonia monitoring
• Set automated alerts when NH3 exceeds safe thresholds
• Log historical data for trend analysis and regulatory reporting
• Trigger aeration, water exchange, or feeding adjustments automatically

Complementary Monitoring

For comprehensive nitrogen cycle management, pair the NH3-100 with:

• NH4-100: Monitor total ammonium for complete nitrogen tracking
• pH sensor (PH-100): pH directly affects NH3/NH4⁺ ratio
• DO sensor (DO-100): Oxygen levels affect nitrification efficiency
• Temperature probe: Temperature affects both toxicity and bacterial activity
• NO2-100 / NO3-100: Track nitrite and nitrate for full nitrification monitoring