There are many options for monitoring your homemade hydroponic system. I have put these in order of importance for your system. Please note that for optimal produce and commercial systems all of these are important.
The concentration of nutrients in a solution is measured as Conductivity Factor (CF), the more nutrients in a solution, the more conductive the solution becomes. The CF level of your hydroponic solution is the most important to control; it is actually possible to starve your plants by having too higher nutrient concentration, this process is called reverse osmosis (some weed killers use this method)
CF Meters range hugely in price, models can be found from around $100 for a hand held model to many thousands of dollars for fully automated CF control systems.
CF Meters can be purchased from Amazon, click here for the CF meter I use Blue Lab Commercial Truncheon PPM / EC / CF Meter
Litmus Paper / pH Meter
The acidity / alkalinity of your nutrient solution is measured as pH. Pure water has a pH of around 7, acidic solutions have a pH below 7 and alkaline have a pH above 7.
The pH level of your nutient solution is the second most important. Different minerals in the solution are released at different acidity levels, there is a chart showing the absorption levels here . A pH range between 5.8 and 6.3 is good for most plants.
Litmus Paper is a very cheap way of checking the pH level of a solution. A paper strip is dipped into the hydroponic solution and it will change color. Litmus Paper comes with a color chart, the strip is compared to the color chart, this will show the pH of the solution.
A pH Meter performs the same task as Litmus paper, the meters do cost a lot more than Litmus Paper. Most pH meters have a sensor probe and digital display. The sensor is placed into the hydroponic solution for a specified time and the pH level will be displayed on the meter. The sesor probe on pH Meters normally need to be re-calibrated regularly, a calibration solution is provided with most sensors, this solution is at a know pH level allowing you to calibrate the meter.
Combination meters are available and generally work out much more cost efficient than purchasing the meters individually. The displayed model is available on Amazon, click here to go directly to the Amazon page Bluelab Combo Meter pH, Conductivity and Temperature Monitor
Plants breath carbon dioxide (CO2) and need for photosynthesis. CO2 is present in relatively low quantities, 300-450 Parts Per Million (ppm) in the air. Plant growth can be increased and accelerated by as much as 35% if the level of CO2 is increased to 1500 ppm.
There are several basic CO2 systems that you can easily build or buy
The CO2 systems used in fish tanks can be used. Place the CO2 dispersion unit into a container of water. These units can be purchased from Amazon, click this link to be taken directly to the page on Amazon Hagen Nutrafin CO2 Natural Plant System with CO2 Activator and Stabilizer
Using a plastic soda bottle, a soft plastic tube and a small container. Drill a hole in the lid of the soda bottle and carefully glue the tubing into it, making sure the hole is completely sealed. Glue the other end of the piping into the bottom of the container. Put several inches of water into the container, ensure that the end of the pipe is fully submerged. Put a cup full of sugar and two teaspoons of yeast into the soda bottle and fill to around 1/2 way with warm water. As the mixture ferments, CO2 will be produced and slowly released through the water.
Oil Lamp / Candle
The most simple CO2 is an oil lamp or candle (tea lites are good and burn for a long time), as these burn, CO2 is released. Please remember that fire can be dangerous, ensure that you have these well away from anything flammable.
For larger scale glasshouses CO2 can also be purchased in gas tanks and be released into the growing environment using regulators and solenoid valves.
Small CO2 gas bottle systems used in fish tanks can also be purchased from Amazon, these are good in a small enclosure. Click here to go directly to the page on Amazon Fluval Mini Pressurized 20g-CO2 Kit – 0.7 ounces
A thermostat is used to regulate the temperature of your glasshouse, they can be used to automatically open and shut windows, run fans and control heaters.