A comparison of two pH-stat carbon dioxide dosing systems for ocean acidification experiments

As the oceans acidify due to increasing atmospheric CO₂, there is a growing need to understand the impact of this process on marine organisms. Field observations are difficult because of multiple covarying factors (e.g., temperature, salinity). As such, there is interest in conducting controlled, laboratory experiments to best understand how changes in acidity will affect marine organisms. We tested two intermittent CO₂ dosing systems, a "home aquarium hobby" grade pH controller and an industrial process control platform. We assessed stability, accuracy, and precision over 7-d experimental periods as well as relative cost of the two configurations. We also compared three laboratory-grade pH electrodes to the hobbyist electrode to further evaluate electrode quality on systemcontrolled pH stability and drift. Whereas the industrial system offered some benefit with regard to autonomy, our results show that the low-cost hobbyist system can be modified appropriately to provide comparable pH control. We provide a detailed list of procedures and software developed for the implementation of a cost-effective, precision-controlled CO₂ dosing system to support laboratory-based ocean acidification experiments.