I created this to get an accurate reading of the color of CO2 Indicator for a planted freshwater aquarium control system and get alerts if it turns too yellow. It's also useful for recording samples when testing for ammonia, nitrates etc. This was built for the Krill software platform I maintain which can read the color of the inserted sample and send alerts if it falls withing a color range. Blog post about this project is here: https://krillswarm.com/posts/2026/04/05/co2-reactor-sensor/