# CO2 Placement



## Zabman14u (Jun 20, 2009)

i just got done building a CO2 reactor using the one mentionedhttp://www.aquaticplantcentral.com/forumapc/diy-aquarium-projects/44053-tiny-super-efficient-co2-reactor.html and got to thinking, is it best to put one of these style pumps in the upper level of the tank, mid range, lower in the tank or does it really not make any difference as the water is moving around so much. my thinking is that since CO2 is heavier than O2 (if i remembered my chemistry right) that it would be best to put it at the higher level of the tank where it would let the CO2 settle down. it also requires less pressure to pump the CO2 into the tank as is not as deep in the water (i have a 30 gal tank). but then i also gotten to think that it is still bubbles and they rise to the surface and putting them at the top of the tank it would have less time to dissolve into the water. im using a DIY CO2 generator and didnt know what other people have found. thanks


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## armedbiggiet (May 6, 2006)

DO you mean the liquid form is heaver? CO2 escape out of the water way faster than O2... like 10 times or more. That is why those BB gun was never made for using O2. When I still using DIY I use a power pump to shot out and the bulbs dos need some time to dissolve.


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## Zabman14u (Jun 20, 2009)

ok thanks. i was under the impression that the gas form was heavier. maybe its just a factor in the dissolvetion rate into water?


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## pepetj (Oct 2, 2008)

The info I am providing is based on my own experience, observations, and what I've read around, mostly here at APC.

At first I used the unreliable charts of pH and KH to estimate levels of dissolved CO2 (like the one in Tetra Laborett test kit). Then I went to build my own DIY CO2 drop checkers, which have an expected error of measurement as high as 36% but still useful for our purposes. Finally I got a dissolved CO2 test kit from Hach.

With the yeast-sugar-baking soda DIY CO2 generator (2 or 3 2L bottles)-gas separator (20oz bottle)-reactor (tiny efficient Elite Mini filter with a broken end of Chinese food wooden stick attached to the end of the hose) I manage to get 12ppm of CO2 at lights-on/noon and 24ppm at lights-off/midnite (I placed an airpump with a timer for the lights-off period). I assume that the plants (and other forms of life) are using up the differential since the DIY system runs 24/7. The way my plants are responding is great.

Keeping minimal water surface agitation while keeping adequate levels of dissolved oxygen for our fish to thrive (not just survive) is a hit-and-miss (trial and error) experience. That meant removing (or downgrading the flow rate of) HOBs and using wet/dry sump, canister, or sponge filtration.

I use a quite complicated test for dissolved oxygen (Hach) to measure when in doubt (e.g. have to have the sample water flooding the glass vase for 10 minutes with minimal flow before testing). But I only test for those tanks with delicate fish.

O2 and CO2 do not out-compete each other as dissolved gases in the water column but water agitation will increase the level of dissolved O2 while decreases CO2. This usually means that mechanical filtration should be at low-end which ends up requiring a somewhat careful removal of organic solid waste being performed at water changes.

This is what I have found to be useful in staying within a zone of safety:

Ideal dissolved levels for CO2 drop pH by a full point (e.g. from 7.8 to 6.8 in my tanks). Simply put, monitor the pH of the tank, if your pH doesn't reach a full point drop, your level of dissolved CO2 should be safe for most fish (some delicate fish require somewhat high levels of dissolved oxygen). I do my best to prevent pH falling below that "one full point drop reference" by...

Monitoring the KH. I aim at keeping KH variations from 3.5 to 2.0 dKH (3.5 after partial water change, 2.0 prior to water change). I use some peat fiber (for some reason pellets of peat fiber don't get as good results as loose peat fiber in my tanks) to further reach the target of pH/KH in the tanks I want soft/acidic water, but for standard settings I go without peat.

Note also that an upgrade in lighting is usually needed when injecting CO2.

Pepetj
Santo Domingo


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## JeffyFunk (Apr 6, 2006)

Zabman14u said:


> ... since CO2 is heavier than O2 (if i remembered my chemistry right) that it would be best to put it at the higher level of the tank where it would let the CO2 settle down....


Is CO2 more dense than air? Yes. However, that is not the important thing here. The important fact is that CO2 (or any gas @ standard temperature pressure, really) is that it is *less* dense than water so it will rise in the tank.

The issue of where people place their CO2 distribution is actually something that I've been thinking about a lot lately (and still don't know the answer to). My guess is that the lower in the tank you can place it (where "it" is your CO2 distribution method or outlet), the better since then the CO2 gas then has more time to dissolve by having more time to (theoretically) move around the tank more. I think it'd be interesting to hear where other people place their reactor outlets.


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## armedbiggiet (May 6, 2006)

Yeah, like alll ADA tanks they all put there diffuser half way in the tank. Maybe it is just for photo shoot.


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