Measuring pH Concentration In Aquaculture

Introduction

Figure 1: The aquaculture industry plays an important role in the economy and food security.

The role of pH concentration in aquaculture is a critical factor that influences the health and growth of aquatic organisms. Maintaining the correct pH balance is essential for ensuring optimal water quality, as it affects various biological processes such as metabolism, reproduction, and immune response. Traditional methods of measuring pH can be time-consuming and may not provide the real-time data necessary for precise management. The use of Visible Near-Infrared (Vis-NIR) spectroscopy presents a non-invasive, rapid, and accurate alternative for monitoring pH levels. This technology leverages the absorption characteristics of water to detect changes in pH, offering aquaculture operators the ability to make immediate adjustments to their water management practices, thus promoting a healthier and more sustainable aquaculture environment.

pH Environment for Aquatic Organisms        

Figure 2: For different types of aquatic products, different pH concentrations in the water will be required.

The pH level of water is a critical factor in aquaculture, influencing the health, growth, and reproduction of aquatic organisms. Different species have specific pH tolerance ranges.

• Freshwater Fish: Most freshwater fish thrive in a slightly acidic to neutral pH range of 6.5 to 7.5. However, species like catfish can tolerate slightly higher pH levels.
• Saltwater Fish: Marine environments typically have a higher pH, ranging from 7.8 to 8.4. However, specific species may have narrower pH tolerances.
• Shrimp and Prawns: These crustaceans prefer slightly alkaline water with a pH range of 7.5 to 8.5.
• Mollusks: Oysters, clams, and mussels generally thrive in slightly alkaline conditions with a pH range of 7.8 to 8.2.

It's essential to note that these are general guidelines, and optimal pH levels can vary depending on factors such as water temperature, salinity, and the specific species being cultured. Maintaining a stable pH within the desired range is crucial for the overall health and productivity of an aquaculture system.

Method

When light interacts with a sample, it can be absorbed, transmitted, or reflected. VIS-NIR spectroscopy measures these interactions to provide information about the sample's composition and properties.

• Absorption spectroscopy: Measures the amount of light absorbed by a sample at different wavelengths.
• Reflectance spectroscopy: Measures the amount of light reflected by a sample's surface.
• Transmittance spectroscopy: Measures the amount of light passing through a sample.

While VIS-NIR spectroscopy cannot directly measure pH due to strong water absorption, it can be used indirectly by employing pH indicators. Here's a general outline of the steps involved:

1. Indicator Selection: Choose a pH indicator suitable for the desired pH range. The indicator should exhibit distinct spectral changes with varying pH levels.
2. Standard Solution Preparation: Prepare a series of standard solutions with known pH values covering the desired range.
3. Spectra Acquisition: Add the selected pH indicator to each standard solution and measure their absorbance spectra using a VIS-NIR spectrometer.
4. Calibration Curve Development: Create a calibration curve by plotting the absorbance at specific wavelengths against the known pH values of the standard solutions.
5. Sample Preparation: Add the pH indicator to the aquaculture water sample.
6. Sample Measurement: Measure the absorbance spectrum of the water sample using the same spectrometer and conditions as for the calibration curve.
7. pH Determination: Use the calibration curve to estimate the pH value of the water sample based on its absorbance spectrum.

Result

In a specific case, phenol red was utilized as a pH indicator to assess the acidity or basicity of various water samples. The pH range suitable for phenol red is between 6 and 8.2, which aligns with the typical pH levels of environmental water samples. A spectrophotometer measured the absorbance values, which were then plotted on a graph (Figure 3). The resulting graph demonstrated a clear correlation between the absorbance levels and the pH values, confirming the reliability of phenol red as an indicator within the specified range.

Figure 3: Spectral graphs of water samples with different pH.

Measurement system

Ocean Insight's HR6 spectrometer coupled with the HL-2000 light source offers a robust solution for indirect pH measurement in aquaculture.

Figure 4: The Ocean SR spectrophotometer.

The Ocean SR6 spectrometer stands out in the field of aquaculture for its exceptional capabilities in measuring pH concentration, a critical parameter for maintaining the health of aquatic ecosystems. With a wavelength range of approximately 185-1100 nm, it offers high flexibility for various light absorption measurements. The optical resolution, configurable down to 0.50 nm with a 25 µm slit, ensures precise spectral data, which is vital for accurate pH monitoring. Its high sensitivity, demonstrated by a signal-to-noise ratio of up to 3500:1 with High-Speed Averaging Mode, allows for the detection of even the most subtle changes in sample composition. The SR6's versatility is further enhanced by its robust design, capable of operating within a wide temperature range, making it suitable for both controlled laboratory environments and challenging industrial settings. These features, combined with its compact size and ease of integration with various accessories, make the Ocean SR6 an invaluable tool for ensuring the quality and sustainability of aquaculture practices.

Figure 5: HL-2000 Light Source.

The HL-2000 light source is a versatile tool in the aquaculture industry, offering a wide wavelength range from 360 to 2500 nm, which is essential for accurate pH concentration measurements. Its high stability, with less than 0.3% drift per hour, ensures consistent performance over time. The high-power version, HL-2000-HP, is particularly beneficial for applications requiring strong VIS-NIR output, utilizing a 20-watt bulb for enhanced illumination. These features, combined with a long-life bulb option that provides up to 10,000 hours of use, make the HL-2000 series a reliable choice for precise and efficient optical analysis.

Conclusion

The use of Visible Near-Infrared (Vis-NIR) spectroscopy in aquaculture offers a non-invasive, rapid, and accurate method for monitoring pH levels. This technology enables real-time adjustments to water management practices, promoting a healthier and more sustainable environment for aquatic organisms. The Ocean Insight’s HR6 spectrometer and HL-2000 light source provide robust solutions for precise pH measurement, ensuring the quality and productivity of aquaculture systems. By leveraging these advanced tools, aquaculture operators can maintain optimal water conditions, enhancing the overall health and growth of their aquatic species.