It’s challenging with a small tank getting the CO2 flow to be both low and stable. I use 600g disposable CO2 cylinders with a single stage regulator that is ok, but not very useful for fine control. There are several downstream valves that further reduce the gas flow. The CO2 over the last month or so has been fine, but yesterday and a few days before the flow has been creeping upwards as measured by the bubble counter and today was coming through more than what I’d like, with the drop checker appearing the morning after a 50% water change a little aggressively pale in what might be the 35 ppm CO2 range – that’s ok for today but could be problematic at this rate over the next few days. I adjusted the CO2 at the regulator down from 10 L/min to 8 L/min – going much lower than this is quite unreliable – then tweaked the downstream controls to get back to 120 bubbles / min which is about right. Something to keep an eye on over the next few days.