CO2 reactor/diffuser redundancy

[carlfsk]

Hi guys, just for discussion. Have anyone thought of injecting CO2 into the tank through the inflow tube? In this manner, the CO2 will be fully dissolved inside the canister before it flows back into the tank.

Initially my thought is whether the CO2 injected and at the same time dissolved within the canister, will it cause corrosion or whatever damages to it and resulting it’s malfunction? However on second thoughts, even if a diffuser/reactor is used in the tank, the water with dissolved CO2 will still flow back into the canister thus rendering damages, if it does. SO it’s back to square one.

If it’s the same whether we inject CO2 through the canister’s inflow tube or in tank througha diffuser/reactor, then why are we still using a reactor/diffusor then?

Would you like to discuss on this?

[FC]

Carl,

Good question.

I had used this method before, it is working. The only concern about this method of dissolving CO2 is:
1) The acidity of the water going into the canister where benificial bacterial is living
2) The efficiency of CO2 dissolve rate

So, before you embark on it, there is a few considerations :
1) The tank size
2) The canister filter size, flowrate and media used
3) Rate of CO2 injection

The tank size determines the CO2 injection rate and the filter flow rate affect the concentration of the CO2 being flow into the canister. The filter size and media affect the efficiency of the CO2 dissolve rate and air traps.

Example
For my tank:
1) 360 litre (nett water volume)
2) Eheim 2080 with media capacity of 7.2 litre and flow rate of 1050 litre/hr
3) CO2 injection rate of 6 bubbles per second rate

Results:
With CO2 injected at the filter's inlet, the acidity going into the filter is about 6~6.2 which is fine to the bacteria. The water column is about 6.2~6.4. The efficiency of the CO2 dissolve rate is about 90% (guess work), there is still bubbles comming out of the outlet.

I would say it is the right balance and it works fine.

End.
++

Tips. Use only 1 layer of the fine filter floss because it traps the undissolved CO2 impurities (mainly Nitrogen). Or better, don't use it at all.

[carlfsk]

Hi Freddy, thanks for the informative response. At least now I'm more convince it works.

OK. I intend to use it on a 140 litres tank (5ft by 1ft by 1ft). Currently using the Dennerle cyclo 5000 reactor running on the Rena XP3 (flow rate should be around 1300 litres/hr. I thought it will be too strong but seems fine to me when it's running. Just installed the Rena only yesterday. Formally I was using Eheim eco2231...such a big jump...After a while I saw some bubbles coming from the lawn of hair grass which has never happen before. The increased water flow with CO2 does make a diffences.

But now I was thinking to get as much equipment out of the tank as possible. A hobbyist gave me this idea of injecting the CO2 into the canister. And I thought what a great idea. I'm gonna try that real soon.

A caveat raised by another hobbyist in another forum. He mentioned if the CO2 dissovle rate is too low in the canister, the undissolved bubbles of CO2 will spoil the impeller. Too much undissolved bubbles will result in a scenario where the impeller is running without any water/in the air. Any comments on this thought?

[carlfsk]

Oh almost forget. Freddy, you mentioned using only a layer of filter floss to prevent too much CO2 impurities from trapping. I suppose those filter sponge used in eheim filter will trap CO2 impurities too, right?

So your suggestion is only to use filter media such as biohome, ceramic rings etc without those floss or sponge? In this case, where does the 'mechanical' filteration sets in? Won't the shit or dirt be flowing back to the tank without these filter floss and sponge?

Thanks.

Just for discussion.

[timebomb]

In this case, where does the 'mechanical' filteration sets in? Won't the shit or dirt be flowing back to the tank without these filter floss and sponge?

Carl, filter floss traps the small particles but they won't stop the fine ones from flowing back into your tank. A planted tank does not need fine filtration as the fine particles will settle on the gravel or get trapped by the plants. I use 2 Eheims for my 4 feet tank but I don't have filter floss or sponge inside either of them. The water in the tank remains just as clear.

If you're going to run your CO2 into your filter, there's a danger you will trap an air pocket inside it. Those of us who are using reactors like the spiralling glass tubes know that not all the CO2 can be dissolved. In fact, I kind of suspect that what we think is pure CO2 in the gas tank actually consists of many other gases.

Loh K L

[PeterGwee]

Carl, filter canisters are simply not the most efficient CO2 reactors in my opinion. You are better off getting a powerhead that circulates 2-4x the volume of your tank, feed the CO2 into the intake (impeller smashes the CO2 bubbles into very fine ones...smaller bubbles dissolves faster due to more surface area of contact.), feed the output of the powerhead to the Dennerle cyclo 5000 reactor and finally connect the output from the reactor to a rainbar and attach it across the entire bottom back of tank (facing the front). This is about the best flow pattern that I have seen and its Tom Barr's idea (Plant guru with loads of experience and knowledge). Note that a reactor works best with more flow till the point where the bubbles bypass the reactor in a very short time. So..the notion is more flow = better mixing and response time.

Do take note that the powerhead method requires the position of the powerhead such that the intake is facing the surface of the water so as to burp out the bubbles once the powerhead is off. This prevents the powerhead from air-locking once it is started up the next day or so. The Dennerle cyclo 5000 reactor has a CO2 injection point that needs to be tied off when using the method suggested either by means of a check valve or whichever method deem possible.

Regards
Peter Gwee :wink:

[FC]

OK. I intend to use it on a 140 litres tank (5ft by 1ft by 1ft). Currently using the Dennerle cyclo 5000 reactor running on the Rena XP3 (flow rate should be around 1300 litres/hr.

the undissolved bubbles of CO2 will spoil the impeller.

Carl,
Don't worry on the impeller at all, your filter flow rate and capacity vs your tank size is ideal for such method of CO2 injection; the flow rate is enough to keep the air out of the impeller and its' shaft.

But now I was thinking to get as much equipment out of the tank as possible.

That is my ideal too and any professionally setup tank would like to have minimum equipment in the tank.

I suppose those filter sponge used in eheim filter will trap CO2 impurities too, right?

This one is ok, it is much porous that the floss. In fact it helps to dissolve the CO2 better by trapping it for a short while.

Won't the shit or dirt be flowing back to the tank without these filter floss and sponge?

There is no filter other that the diatom filter can effectively trap fine dirt, the dirt simply circulate in the tank, causing cloudiness. Like Kwek Leong mentioned, a clear/good water tank is one that allows the fine particles to settle down to the bed of the tank. Place the filter outlet such that it flow along the long side of the tank's wall, this will minimise turbulance. It should create only a mild stir in the tank, thus, encouraging the fine dirt to settle down.

Pack the filter with the usual media like ceramic rings (at the bottom) and bio substrate, etc. Place the sponge at the middle or top.

[Ptarmigan]

3) CO2 injection rate of 6 bubbles per second rate

Hi Freddy, I wonder if you have measured what the volume one of your bubbles is ? In other words, I would be interested to know what volume of CO2 is entering your tank each second ?

The reason I ask is that I have experimented with various methods of CO2 injection and currently I use an up-side-down dome/chamber, (half of a cut off plastic fizzy drink bottle ! )
So I can estimate the volume of CO2 being dissolved, ( by the rate at which the level receeds back up the chamber, pi.R^2.L and all that !! ) but I am not sure about my exact PH/KH measurements, so I need a "reality-check" with the volume of CO2 that other people are using for their various tank sizes and water conditions.

thanks,
Malcolm.

[FC]

Hi Malcolm,

Just a guessetimation, it is about 7~8 cubic mm.

Based on your chamber method which dissolve CO2 by water pressure and diffusion, I guess you are having a small tank and using the yeast method. To set the rate of CO2 injection, other than by CO2 volume, it is more practical to adjust the immerse dept of the chamber.

Feel free to ask more questions.

[Ptarmigan]

Thanks for the info. Freddy,

Just a guessetimation, it is about 7~8 cubic mm.

oops, sorry, I'm a little confused !
is that per bubble?
or is it the total per second (ie the total of 6 bubbles) ??

Hmmm, let's think,,, if your bubbles are about 2mm dia then 4/3.pi.r^3 =~ 4 cu.mm
so I guess it is per bubble and your bubbles are a fraction larger than 2mm ???

Based on your chamber method which dissolve CO2 by water pressure and diffusion,
I guess you are having a small tank and using the yeast method.

The tank is 1.5m x 38cm by 35cm(depth of water), about 200L I think if my maths is right !!
and the chamber is mostly cylindrical 10cm dia by about 15cm high (plus a dome on top - it used to be a plastic beer bottle I think !)
The chamber is not quite totally submerged, the top of the chamber is touching the cover glass.

I periodically, manually, fill the chamber with CO2 from a modified fizzydrink maker.(airline tube between the injector of the fizzy machine and the chamber)
hey kids - dont do this at home by yourselves, ask your parent or guardian first !! :wink:
This chamberfull will last anywhere between about 5hours and 1 hour depending on the waterflow near the orifice, hence my request for a "reality check" !

In still water conditions it lasts about 5 hours, but if I direct the output of a filter or power head past the contraption then the rate is increased dramatically. ( the filter outlet is mid-level to avoid surface turbulence and consequent loss of CO2 )

To have the full chamber dissolved in just 1hr seemed to me to be a lot of gas ! The plants seem to enjoy it and it does not distress the fish. However, I have erred on the side of caution and usually run it at about a 3 or 4hr period.
So, my shedule is to fill it once in the morning and once in the afternoon (low light levels) and two or three times during the evening/night when all the lights are on.

OK, so now I'm going to go to my pocket calculator and make with some sums to compare your rate in 360L with my various rates in 200L -->>>

PS I used to use a yeast method involving two 5L and one 2L bottles, but it was all very unpredictable and "iffy", I sometimes still use those as a suplementary 'background' CO2 level but generally prefer to use my yeasties to make beer not burps :-)

Thanks,
Malcolm.

[FC]

Malcolm,

Sorry, it is about 7~8 cubic mm per bubble.