Thought we'd share a small technical update...
We've been running a Ca reactor to keep calcium and alkalinity stable for several years. We switched from a smaller Deltec Ca reactor to the GEO 818 a couple of years ago and also run a GEO Kalk reactor to help mitigate the lower pH associated with running a calcium reactor. Over the past 2 years, the demand for Ca and alkalinity in our system has increased significantly and we eventually reached a point where we were topping off with 100% kalk.
After a kalk over dose scare in November of last year, we made the decision to separate Kalk dosing from our fresh water top-off and as a result, made it more difficult to keep our pH in an acceptable range (dropping into the lower 7.7's).
Of course we tried some obvious things (pulling in fresh air, adding air stones to our sumps and running the lights for the frag tank/refugium at night) with no discernible difference in pH.
After looking at several options, we decided to setup CO2 scrubbers using soda lime. If you've not seen this, it's a granular hygroscopic calcium hydroxide used in CO2 absorption applications like SCUBA rebreathers. We placed the dry media into our TLF reactors which we then connected to the air intakes on our skimmers. A CO2 scrubber does not remove CO2 from the water column, rather it reduces CO2 in the air that passes through the reactor and into a skimmer.
We have been running the CO2 scrubbers on both of our skimmers for approx 3 months now with good results. The night time low normally stays in the lower 8.0's range and occasionally will dip into the upper 7.9's. The daytime pH ranges between 8.2 and 8.25 - We can live with that!
We purchased a 5g bucket of medical soda lime which should last several months. We replace the granules when the media is exhausted (media turns blue) which is approx every 2.5 to 3 weeks.