# Water IoT Monitoring System for Aquaponics Health and Fishery Applications
## 3 Materials and Methods
### Water Monitoring Parameters  
There is a set of water probes which can be used to build a digital health monitoring system. Most probes are used for the detection of one or more water metrics such as pH, temperature, and ammonia, etc. These probes consist of two interfaces; the first interface reacts with water, based on physical or chemical principles to produce the values of the metric(s). The second interface is an electrical interface used to allow a digital system to retrieve the measured metrics. The key aspect to consider in the selection of water probes are:  
1. The time elapsed between each required calibration;
2. The accuracy of the measured metric;
3. The duration until water probe is not functional (lasting period).  
These aspects directly influence the operational aspects of the deployed system. Other aspects such as the electrical interface have more engineering requirements, which will directly affect the final cost of the system. The number of metrics to be monitored will also have an impact on the quality and cost of the developed monitoring system, since each monitored metric/parameter will have an associated direct cost. There is a non-exhaustive list of water probes in the market which can be used to enhance the capabilities of the digital health monitoring system for aquaponics.  
The following are parameters or metrics for monitoring water, soil, and air quality. For water quality monitoring:  
1. Potential of Hydrogen (\(pH\)): this is a scale used to specify the acidity or basicity of an aqueous solution [22];
2. Water Temperature: temperature of the water;
3. Dissolved Oxygen (\(DO\)): this is the amount of gaseous oxygen (\(O_{2}\)) dissolved in the water [23];
4. Oxidation-Reduction Potential (\(ORP\)): this is a measure of the tendency of a chemical specie to acquire electrons from or lose electrons to an electrode thereby reduced or oxydised, respectively [24];
5. Electrical Conductivity (\(EC\)): this is the measure of the amount of electrical current a material can carry or its ability to carry a current [25];
6. Total Dissolved Solids (\(TDS\)): this is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionised, or micro-granular (colloidal sol) suspended form [26];
7. Total suspended solids (\(TSS\)): this is the dry weight of suspended particles that are not dissolved in a sample of water and that can be trapped by a filter that is analysed using a filtration apparatus [27];
8. Water Level (\(WL\)): this is the level of water along a given surface (e.g., fishpond);
9. Water Flow (\(WF\)): this is the speed of the water across the pipeline circuit;
10. Ion-Selective Ammonia (\(NH_{4}^{+}\)): this is the concentration of \(NH_{4}^{+}\) in aqueous solutions;
11. Ion-Selective Nitrite (\(NO_{2}^{-}\)): this is the concentration of \(NO_{2}^{-}\) in aqueous solutions;
12. Ion-Selective Nitrate (\(NO_{3}^{-}\)): this is the concentration of \(NO_{3}^{-}\) in aqueous solutions.  
Here, it is worth emphasising that the hydroponics metrics (i.e., ORP, pH, EC, Temp) and the aquaponics metrics (i.e., \(NH_{4}^{+}\), \(NO_{2}^{-}\), and \(NO_{3}^{-}\)) are the main metrics to control the aquaponic cycle.  
We have also considered other metrics for soil and air quality monitoring:  
1. Light Intensity (\(LI\)): it measures the number of lux to determine suitability to carry out photosynthesis processes in plants;
2. Air Temperature (\(AT\)): it is the temperature of the air;
3. Air Humidity (\(AH\)): it is the humidity of the air;
4. Wind Direction and Speed (\(WDS\)): it is the speed of winds;
5. Soil Moisture (\(SM\)): it is the level of water in-between soil particles.