A recent product called the CO2 Scubber from MCU Research has re-sparked my own interest into a chemical mixture that I experimented with years ago–Soda lime. Soda lime is a blend of Calcium Hydroxide (Kalkwasser), Sodium Hydroxide, Potassium Hydroxide and water in a “dry” granular form. This mixture is used in many medical, military, and safety [...]
A recent product called the CO2 Scubber from MCU Research has re-sparked my own interest into a chemical mixture that I experimented with years ago–Soda lime. Soda lime is a blend of Calcium Hydroxide (Kalkwasser), Sodium Hydroxide, Potassium Hydroxide and water in a “dry” granular form. This mixture is used in many medical, military, and safety applications for its ability to absorb CO2. Soda lime absorbs CO2 like Kalkwasser does when added directly to aquarium water for calcium and alkalinity supplementation.
Calcium hydroxide (kalkwasser) actually “captures” CO2 to alleviate the pH suppression when added to our aquariums– shown below we see that the addition of calcium hydroxide (CaOH) uses CO2 and forms calcium and bicarbonate (alkalinity) in red.
Ca++ + 2(OH-) + 2(CO2) <–> Ca++ + 2(HCO3-)
Notice one of the ingredients of Soda lime is water. This is what allows the Calcium and other hydroxide to absorb CO2 into a stable solid. In that sense, you’re better off using kalkwasser as it is traditionally used in top off water. It can relieve pH suppression from excess CO2 while also completing calcium / alkalinity supplementation and evaporation requirements. Additionally it has the propensity to precipitate phosphates, making it superior in nearly all ways for aquarium use when added to the water versus filtering air.
However, if you prefer to not use Kalkwasser then Soda lime may have an application by filtering air and removing carbon dioxide prior to entering the skimmer. Soda Lime is no secret to scuba divers–it is a main component in closed circuit rebreathers and is commonly refered to as a CO2 scrubber in other industries. (See howstuffworks’ explanation on its use in scuba diving). Some popular brands of Soda lime include Dragersorb, Sofnolime, ExtendAIR, and Spherasorb. A few of these brands offer color changing media, that indicates when the Soda lime is exhausted and can no longer absorb CO2. These range in price, but can be found online or at specialty scuba stores for $50-$100+ for 5L of the dry media.
MCU states pH values increase on average “.o5 to .23″ points and the media lasts 1-3 months. Interestingly the MCU media changes from white to blue / purple much like the offerings for CCR such as Sperasorb. Coincidence? We can’t say, but like most aquarium products Soda lime is not exclusive to this industry.
When I tested Soda Lime it was years ago on a then-state-of-the-art ETSS downdraft skimmer. During the summer months I would grill outdoors quite a bit, however the grill was in close proximity to a window that entered the room of the tank. After a previous experience from outdoor paint fumes entering the house and creating a skimmer overflow, I became aware of the effect air pollution can have on skimmer performance. Worried about this, I created a solution to the filter the air thanks to funnel and nylon mesh.
To filter the air I used activated carbon and filter floss in the funnel. This would remove the majority of contaminants (after all most aquarium marketed activated carbons are actually made to filter air). Not satisfied with carbon alone, I also added Soda lime that I had on hand from a chemistry class. In that class I learned of its effects on CO2 and it came in handy. The large opening of the funnel held the media which was not able to escape out the small opening thanks to the mesh. The funnel output was then connected to the skimmers air intake–simple and made from spare parts around the house.
The pH relief was nothing to be excited about. After all I had the windows open and was dosing kalkwasser, leaving no room for the Soda lime to show effect. However, as I find myself shifted from suburbia to the city… cracking open a window is less of an option. Maybe I’ll give it another try.
I was not the first to try Soda Lime on a skimmer–it was discussed on various forums and chats in the 90s. Original or not, MCU has an interesting product. The literature states ”Patent Pending” on their $80 co2 scrubber (replacements cost $29.99). I am curious to see how their patent experience will unfold and how the aquarium market responds. You can find more info on the product at MCU’s website.
