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CO2 Indicators

Note: you can build your own CO2 indicator by constructing just the mechanical PVC/bottle part of Gary Bishop's CO2 controller.


  1. RE: CO2 devices
    by Khew Sin Sun <khewss/> (Sat, 30 Jan 1999)
  2. RE: CO2 devices
    by "James Purchase" <jpurch/> (Fri, 29 Jan 1999)

RE: CO2 devices

by Khew Sin Sun <khewss/>
Date: Sat, 30 Jan 1999

>I haven't seen the Sera unit, but I do have, and use both the Dupla and the

I used the Sera unit before i ended up with the Dupla one. I found the Sera
"casing" a drag,because it fits too tightly!! It's so tight that when u
need to re-fill (or bleach it to get the algae out) i had to use a pair of
pliers to pry open the cap!! Having your hands wet,didn't help at all as it
makes things more slippery! Unfortunately,u'd HAVE to get your hands wet to
remove the Sera unit from the tank in the first place! :-P

I ended up with a Dupla set which was a breeze to use (and open as well!)
I guess the best deal (albeit expensive),is ADA's "teardrop" unit. Just
fill up with your tank water,add the solution and over turn!! ;-)


RE: CO2 devices

by "James Purchase" <jpurch/>
Date: Fri, 29 Jan 1999

Daniel Green seems to have discovered a "new" item -

>For all people out there using uncontrolled yeast co2 there seems to be an
>amazing option.
>For AUS $25 I can mail order a sera permanent co2 test it is some kind of
>colour changing meter that shows if one needs to add/decrease co2

>Any comments on this would be greatly appreciated.

O.K., but remember, you asked.... Actually, there are quite a few products
like this, from a number of companies. Dupla, Eheim and Aqua Design Amano
all make variations on the same theme. It is basically just a submerged
chamber which holds an indicator solution which is pH dependant. It offers
you no real control over your CO2 concentration, it just gives you a
continuous indication of your tank's pH (at a given KH, lower pH values mean
higher CO2 levels in the water).

I haven't seen the Sera unit, but I do have, and use both the Dupla and the
ADA units. The ADA one in particular is a beautiful little bit of glass
blowing, but it suffers from the fact that it is totally transparent and  it
can be hard to tell just what color the indicator fluid is against a dark
background of plants. The Dupla unit, while made of plastic, does have the
advantage of having a white base against which the color change of the
indicator fluid is clearly visible.

I guess they are fine as far as they go, but they don't, in and of
themselves, do anything to control the amount of CO2 in your tank, be it
from compressed gas cylinders or from a yeast reactor.

The archives contains a bit of information on the Dupla unit - check it out.

Kelly Beard is wondering about CO2 reactors -

>I've got an Eheim diffuser.  It's okay, but a lot of those little bubbles
>make it to the surface, so that's wasted CO2.  I was looking at maybe one
>the Dupla reactors, or at least something that might fully incorporate CO2
>into the water, so the only bubbles you see in your tank is the ones your
>plants produce.

Again, one of a number of similar devices - Eheim makes one, Dupla makes
one, and ADA makes a whole series of them, for different sized tanks.
Christopher Coleman ran some comparative tests on the Eheim vs. the ADA
Pollen Glass Diffusers. It should be in the archives.

I have both an Eheim Diffuser and a Dupla Atomizer and they are remarkably
similar, except for the fact that in the Eheim, the diffuser plate rests
"within" the rubber sealing gasket, while in the Dupla Atomizer the diffuser
plate is bigger and there are sealing gaskets both above and below the
actual ceramic disk. I would imagine that if you are seeing mixed sizes of
bubbles being released from the Eheim unit, some gas might be leaking out
between the ceramic disk and the sealing gasket. I would expect the Dupla
unit to produce a more uniform stream of fine bubbles, due to the better
sealing provided by the two rubber gaskets.

Before he ditched the line, J.P.Burleson told me that the Dupla CO2 Atomizer
would be more than capable of supplying CO2 to a 30 U.S. Gallon aquarium,
but would not do so as efficiently as a Dupla Reactor 400. I suppose the
difference is in the CO2 bubbles escaping from the tank undissolved.

CO2 reactors are not really a difficult thing to construct yourself. I
believe that I saw a neat little unit made by Olga Betts in a photograph on
George Booth's site (Olga _still_ doesn't have her own web site). I have one
of identical design (thank's Olga!) in my big tank - and it works very well
(absolutely _no_ fine mist of CO2 bubbles getting into the main water
column). It is easily made using a tube from a gravel washer, some tubing
and suction cups and a power head. Fill the tube with mini bioballs, put
some fine mesh over the open end and away you go.

You could also just use a power head to inject the CO2 into the tank,
relying on the impeller to break up the CO2 into a fine mist. But with this
method, you _will_ see a "fog" of fine bubbles in the tank.

But for a _small_ tank, where space is at a premium, and looks are
important, the DIY option can be ugly. For a tank of 30 U.S. Gallons or
less, I'd rather waste the CO2 and use the very elegant Dupla (or Eheim, or
ADA) atomizers. They are very easily hidden into a back corner close to the
bottom and if the tank has ggod circulation the CO2 bubbles should have
plenty of time to disperse before reaching the water's surface.

By the way, in case anybody is wondering, these Atomizers or Diffusers will
NOT work with Yeast Method CO2. You definately need to use compressed CO2 in
order to achieve the pressure needed to drive the CO2 through the ceramic

James Purchase

Up to CO2 <- Plants <- The Krib This page was last updated 21 February 1999