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[APD] Re: CO2 reactor questions

In my experience, an internal or external CO2 reactor is more efficient than using a cannister filter, but I use both. I curriently use two Eheim 2217s and an Aqua-Medic 1000 for CO2 injection on three tanks. 

Eheims are the only cannisters I have used that will do a decent job as reactors without getting air lock. Fluval MSF filters can't take CO2 injection. I'm not familiar how other brands work besides Eheim and Fluval. Eheims are actually engineered with a channel in the pump head that facilitates gas removal. Eheim obviously designed this with air in mind, but it works for CO2 also, which brings up another benefit of Eheim cannister injection: you don't get a huge buildup of extra gas in the filter so your pH doesn't spike down after the lights go out. The filter simply burps any extra CO2 out.

The gas usage in an Eheim is not too excessive, in my experience. A bubble rate of one per second worked fine in tanks up to 125 gallons and kept the pH in the proper range. My 20# tanks lasted about a year in my 125 gallon. If you live in an area where refills are expensive, you might want to use a reactor, but CO2 is cheap in th US.

The type of Eheim used for CO2 injection is another factor. The Pro I and II series doesn't work nearly as well for CO2 injection vs the 2217/15/13 series. The Pro series uses baskets for holding media and the gas just goes right thru. Very little reaction time. The 22xx series has media that all acts as basically a big plug, holding the gas at the bottom of the filter. There is much less bypass in these vs the Pro series. The Pro series will work (I own both), but the 22xx series is more efficient. 

The main benefit I found in using canister injection vs a reactor was the maintenance of the reactor. There is virtually no maintenance in canister injection, period.  Internal and external reactors need to be cleaned once in a while if they are exposed to light for algae growth inside the chamber. This can be limited if you cover the clear parts of the reactor with an opaque material to limit the growth. I also like that with cannister injection you don't have the plumbing fittings that can leak and the extra heat from another pump or powerhead in the water that you can have with a separate reactor. Feeding off an existing pump can eliminate the heat issue.  Sump placement will also eliminate algae growth inside the reactor, provided the sump is in a dark cabinet. I use an Aqua-Medic 1000 reacor in my 240 gallon tank's sump, and It gets no algae growth.

Cannister injection has worked in a variety of tanks for me up to 125 gallons. It didn't work well at all for me in my 240, and would probably have required two 2217s to function. 

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