CarbonDoser EXT5000 (External Reactor 5000)

(7 reviews)
6.00 LBS
Current Stock:
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CarbonDoser® EXT5000 (External Reactor 5000)

For successfull, efficient introduction of CO2. For aquariums up to 1000 gallons. (or any aquarium with a cannister filter/overflow/remote pump system.
Even though this Reactor is adequate for aquariums up to 1000 gallons, we still highly recommend it for ALL aquarium (with an external filter or pump system) no matter what the size...
All other "inline" reactors rely completely on the flow from the filter...if the flow is not the correct speed, the reactor will not be efficient. This does NOT rely on the filter pump volume, instead includes an internal pump which creates high turbulance of the water & CO2 within the reactor, thereby creating 100% dissolution of the CO2. The design ensures that CO2 can NOT leave the reactor until 100% disolved in the water
We invented and patented this reactor, you will not find a more efficient reactor anywhere
(please indicate Inside Diameter of hose needed. 1/2, 5/8, 3/4, or 1 inch.)
Includes everything you need for installation with the exception of the mounting bracket with screws which is optional.
Watch closely at the video: This is a perfect example of how inefficient and wasteful both glass & ceramic diffusers are. (remember, plants can NOT use CO2 while it is still a bubble. For a plant to absorb CO2, it MUST be totally dissolved (sparged) in the water) If you can see the CO2 bubbles rise to the surface, they're gone and totally wasted.

In extensive testing utilizing the super accurate CarbonDoser® Electronic CO2 Regulator, here are some results (base on maintaining 25 PPM CO2 Saturation):

  • when using the CarbonDoser® EXT 5000 the average settings for a 90 gallon aquarium are:  (1+/-) seconds per bubble/portion @ 8 PSI.)
  • when using the Tunze CO2 Reactor NANO the average setting for a 40 gallon aquarium are:   (2+/-) seconds per bubble/portion @ 6 PSI.)
  • when using a ceramic "diffuser" on a 55 gallon aquarium are:  5 "bubbles per second (not seconds per bubble) @ 35+ PSI. !!!

Basically a ceramic diffuser uses (wastes) a tremendous amount of CO2 compared to a Reactor.

Checkout the videos on youtube... you'll see 1000's of CO2 bubbles flying around the aquarium like a blizzard... "Only sparged (completely dissolved) CO2 is usable to plants.


  • 5
    Carbondoser 5000

    Posted by Kurt Seidler on Jan 3rd 2022

    Glad you changed from a Rio powerhead to a Sicce . I discarded my old Doser because the Rio quit working.

  • 4
    Carbondoser reactor

    Posted by Glenn on Aug 13th 2017

    I have been using this product for about 3 months. It is very efficient in terms of CO2 use. It is well made. Setup is a bit tricky and leaks are a problem if one is not meticulous with the teflon tape or pipe sealent. It is difficult to maintain because it is so tightly sealed. In fact, I still have not figured out how to open it, even with the optional wrench. Update: I figured out how to open it rather easily. Soak the bottom part in hot tap water for 5 to 10 minutes (not the upper part), and it allowed me to open it counter-clockwise relatively easily.

  • 5
    Best Reactor Ever!!!!!!

    Posted by Timothy Haut on Jul 16th 2016

    The way this reactor is designed the CO2 gas is fully disolved in the water before entering the tank. The set up was easy with some assembly required, just make sure to wrap the threads 7 to 8 times with the provided teflon tape and make sure you get a check valve and your in business. If you want to save gas and get quick delivery of gas into your water column this is the top of the line in reactors.

  • 5
    Great product

    Posted by Anthony Tartaglia on Jul 16th 2016

    After many attempts of trying to diffuse C02 into my tank and never being able to achieve the right amount, I was finally sick of wasting money on all these fancy glass and ceramic diffusers so I decided to take Marks advice, he told me I wouldn't be disappointed and it was worth the money, so I finally made the purchase and let me tell you he was right, the plants must have been really C02 deprived because they look amazing now, the Reactor really mixes in the C02 very well with the water before being returned into the tank, and noticed I don't use nearly as much C02 as I was with the other diffusers. for anyone that's going through the same problems I was, this is the answer, like Mark told me you won't be disappointed I now agree 100%.

  • 5
    I was wrong...

    Posted by Shawn McBride on Jun 2nd 2013

    I'm hear to say I was previously wrong about this reactor. I have had the most success while using this reactor. It has out performed diffusers..period. My inexperience earlier in the hobby led me down all kinds of paths and I had once blamed the reactor. I was wrong and am eating crow in this review. I hated the bubbles that made my aquarium look like soda water from the diffusers. Getting adequate levels of CO2 was difficult and used more CO2 with diffusers. This reactor keeps my water clear and the plant growth has been great. I have been so impressed with putting it back on my aquarium I had to come back and share my experience with it. I plan to purchase another one for an upcoming large tank. I currently run this reactor on an ADA 90p which is 48 gallons.

  • 3

    Posted by Unknown on Dec 28th 2010

    Getting the reactor and setting it up was a pain. Not only did it not ship for several weeks (without any notice from, but it arrived with no real instructions. Apparently, they assume expertise with Co2 systems out of all their customers, which I didn't have. Emails to customer servie were never answered (and I don't do phones). After much googling and some trial and error, I was able to set it up. It shouldn't be that way, particularly for a product this expensive. The reactor is working fine, as far as I can tell (plants are pearling nicely, etc), but it's loud, and it has significantly decreased my water flow. Is that normal? Beats me! I certainly haven't gotten any answers from this joint.

  • 5
    Best I have ever used

    Posted by Larry Scofield on Oct 5th 2009

    We have used several reactors, both internal and external. All claiming to be effecient and adequate for large aquariums. We tried the "Aqua-Medic 1000, as well as several others in our 300 gallon aquarium and our 55 gallon. Our aquariums are high light and very heavily planted. NONE of the other reactos come close to this EXT5000. Also, we have noticed a huge difference in CO2 useage/waste as we are using approx 1/2 the amount of CO2. We now have 5 aquariums running with the "'s Ultimate CO2 systems." (make sure you also get the optional "probe holder" so you don't have any "clutter" in your beautifull aquariums !!! thanks for great products