CO2 diffusion - new method?

Hi, I have a pressurised CO2 system in my 240l planted tank. I don't think I'm getting the best of it due to the position of the diffuser - the CO2 is released into the tank (diffuser is at the bottom) and, rather than being dispersed though the tank, most of it is escaping almost immediately.

I have read of a theory (possibly in PFK) of positioning the diffuser just below the intake of the external filter, thus drawing CO2 into the filter where the bubbles are dissolved by the impeller and CO2-rich water is returned to the tank.
Has anyone else heard of this method or had experience of it??

Cheers for any help you can offer......!!

That sounds like a lot of bull if you ask me since the water that comes out of the filter has surface contact. This will only dissapte the CO2 into the air.
What sort of diffuseer are you using?

Hi,

I have heard of that method. However, I'm not sure feeding bubbles into your filter is a good idea. It will be noisy and shorten the life of your impeller.

Do you have much surface disruption, i.e. filter outlet or air stone? If so, this will not help your CO2 absorbtion.

this can cause a problem with the vacuum in the external and stop the external from being primed and pumping water back into tank

The diffuser should be positioned at the lowest part i.e THE BOTTOM of the tank wher the water flow is at its stronges. thus allowing the gas to be absorbed before it reaches the surface. make surs you have the ceramic ring diffuser as this releases a fine mist.

i have fed the Co2 through an external filter for a while with no ill effect on the filter.
The problem with doing this is you dont get a constant flow of Co2 released in to the tank. It comes out in bursts. So instead of the Co2 been released into the tank every second or so it could be every second or every Minuit.
This irregular flow is no good since the Co2 needs to be a stable flow to be any use.
I should mention that the return from the filter was a submerged spray-bar pointing to the bottom of the tank.

I would go with the ceramic diffuser as suggested by russell.

For a 60 gallon tank you really need to use an external CO2 reactor in conjunction with pressurised CO2, this is the most efficient way to inject CO2 in larger tanks, the reactor is plumbed inline with your external cannister filter, a wet and dry filter will not work with CO2 btw, it will keep out gassing the CO2, an ordinary type filter is best, the picture below is one that I have made for a 40 gallon tank, it works well, it needs about 2 bubbles per second to reach 25-30ppm CO2 so its pretty efficient, for a 60 gallon tank you may need to inject about 3 BPS.



You will see in the picture of the reactor the CO2 black tubing comes in at the side about a third of the way down and injects the CO2 directly into the tube, the picture is a bit distorted it looks longer than it is, the reactor is only about 20 inches in length, the water fows in from the top as seen in the picture and the reactor sits underneath the tank in the same position as in the picture, so it sits at a 45 degree angle with the water flowing in from the top from your filter (the reactor gets plumbed in on the return side of the filter) The idea is that as you inject the CO2 into the tube it will want to rise because of gravity, but the water flow coming in from the top will keep pushing the bubble back down and because the diameter of the pvc tube is wider than the filter tubing it slows down the water sufficiently so the bubble just bobs up and down in the pvc tube until it is dissolved into the water, if the tubing was the same diameter as the filter tubing it would not work, the bubble would shoot out the other side because the water pressure remained the same, the water was not slowed down, keeping the tube on its side at a 45 degree angle helps the bubble from shooting straight through also.

The reactor chamber is empty, it is just a hollow pvc tube with the water flowing through, some people put bioballs in them to break up the bubbles, but this dramatically slows down the flow of the filter and IMO is not nescessary, if you make the reactor correctly you do not need the bioballs it functions fine without them.

A ceramic disk on its own will struggle to give you decent amounts of CO2 in a 60 gallon tank, you would need to inject many bubbles per second to get anywhere and as you have already discovered they will more than likely just shoot straight to the top, you really need to use them in conjunction with a lily pipe which gives better flow in a tank and will blow the bubbles around to dissolve them better. A reactor is much more efficient.

I bought all the pieces for the Reactor in B&Q for about €20, the pvc tubing is just standard 40mm.

Very nice system, even though it looks the same as one of the penis pump I was offered recently in a junkmail that got through the firewall...

Very nice system, even though it looks the same as one of the penis pump I was offered recently in a junkmail that got through the firewall...

Don't go near those yokes, the missus insisted I get one, worthless.

Er.... I think I've said too much.

I don't think you are supposed to hook them up to the hoover...

For a 60 gallon tank you really need to use an external CO2 reactor in conjunction with pressurised CO2, this is the most efficient way to inject CO2 in larger tanks, the reactor is plumbed inline with your external cannister filter, a wet and dry filter will not work with CO2 btw, it will keep out gassing the CO2, an ordinary type filter is best, the picture below is one that I have made for a 40 gallon tank, it works well, it needs about 2 bubbles per second to reach 25-30ppm CO2 so its pretty efficient, for a 60 gallon tank you may need to inject about 3 BPS.

You will see in the picture of the reactor the CO2 black tubing comes in at the side about a third of the way down and injects the CO2 directly into the tube, the picture is a bit distorted it looks longer than it is, the reactor is only about 20 inches in length, the water fows in from the top as seen in the picture and the reactor sits underneath the tank in the same position as in the picture, so it sits at a 45 degree angle with the water flowing in from the top from your filter (the reactor gets plumbed in on the return side of the filter) The idea is that as you inject the CO2 into the tube it will want to rise because of gravity, but the water flow coming in from the top will keep pushing the bubble back down and because the diameter of the pvc tube is wider than the filter tubing it slows down the water sufficiently so the bubble just bobs up and down in the pvc tube until it is dissolved into the water, if the tubing was the same diameter as the filter tubing it would not work, the bubble would shoot out the other side because the water pressure remained the same, the water was not slowed down, keeping the tube on its side at a 45 degree angle helps the bubble from shooting straight through also.

The reactor chamber is empty, it is just a hollow pvc tube with the water flowing through, some people put bioballs in them to break up the bubbles, but this dramatically slows down the flow of the filter and IMO is not nescessary, if you make the reactor correctly you do not need the bioballs it functions fine without them.

A ceramic disk on its own will struggle to give you decent amounts of CO2 in a 60 gallon tank, you would need to inject many bubbles per second to get anywhere and as you have already discovered they will more than likely just shoot straight to the top, you really need to use them in conjunction with a lily pipe which gives better flow in a tank and will blow the bubbles around to dissolve them better. A reactor is much more efficient.

I bought all the pieces for the Reactor in B&Q for about €20, the pvc tubing is just standard 40mm.

I probably should have supplied more information. I am using a ceramic diffuser, the tank is filtered by an AQUA ONE CF 1000 and I am using a spray bar, i drilled out the holes in the spray bar wider for less surface disturbance. I have a permanent co2 test the RED SEA one which is telling me my co2 levels are not high enough dispite using 3 bubbles per second. Also i have very little surface disturbance as the spray bar is turned down into the tank. It's just my plant growth is not as good as it once was, I have a heating cable reflectors on my light tubes, laterite but i think it's the diffuser is letting me down.Your reactor looks very interesting and i think i might give it a go, the diffuser is at the lowest point in the tank but even though the bubbles are very small when they reach the top it seems like a waste. THANKS for all your help and info.

hehe.......well I see the boys are getting quite excited by the CO2 reactor

Climbingperch you could also try using a powerhead with the CO2 line attached, some of them come with an air line attachment feature, you hook up the CO2 line and the powerhead impellor should break up the bubbles into a mist and blow them around the tank, if you own a powerhead you could try this, don't know if I would go out and buy one specifically though, but it would probably work a lot better than what you are doing now.

The heating cable won't do anything for you im afraid.

@zig
what flow rate would you suggest?

@zig
what flow rate would you suggest?

Holger I presume you are talking about the CO2 reactor?

New school thinking for planted setups suggests more flow is better, on the 40 gallon that I have that CO2 reactor on I have a eheim 2215 a 2217 would be better though, this would give me about the right amount of flow, about 5-6 times turnover per hour, but the 2215 is fine, with the reactor attached im probably getting 3-4 times turnover per hour, you can begin to get problems in planted tanks when they are heavily grown in, this really reduces the flow in a tank and if you just have barely enough flow to begin with you get dead spots in the tank where algae will break out usually BGA. So more flow is better, but thats the problem with eheims you always have to go for a way bigger filter than the stats tell you, usually the next one up from the normal choice is correct. With the 40 gallon I add a small powerhead when the tank gets really grown in this does the job as well.

The CO2 reactor will definatly reduce flow especially if you add bioballs, the bioballs will reduce flow dramatically probably halve the flow if added, this is another reason the reactor goes on the return side of the filter so the flow going into the impellor is not reduced.

A good rule of thumb is to look at the chart for flow rates choose the one for your tank and then buy the next filter up in the line, this gives you scope to add CO2 reactors and inline heaters as well, overall though you would want to look for about 5 times turnover IMO this would be good.

These type of reactors can be used on huge tanks up to about 300 gallons, they are very common in planted setups, the one I have made is probably the simplest design, just google DIY CO2 reactor and you should get lots of hits for different types all basically do the same thing, just a word of warning it can take quite a while for CO2 to build up when using one of these reactors so some people just let them run 24/7, mine is knocked off for about 6 hours per day via a solenoid and then it runs the rest of the time, they also experience airlocks later in the day and can get a bit noisy, this is true for all CO2 reactors of this type, there is some debate currently what this gas is in the airlock, it is not thought to be CO2 (but maybe it is!) anyway regardless when you have them running properly they give a very even supply of CO2.

You can buy these type of reactors online for stupid amounts of money €60-80 would be normal before postage costs, I could make 5-6 for that amount of money with my design, they are easy to make, use liberal amounts of PVC solvent and it will be waterproof.

I get the principle. I run my 600l tank with what is trmed and HMF filter, essentially a filtermat with a powerhead behind it. Works very well, no maintenance to talk about and is dirt cheap to built. Mine cost about 35€. If you are not sure what I am talking about, google 'Hamburger Mattenfilter' and get it translated by Altavista or any such software. Turnover is 1200l per hour so only twice the volume of the tank and not the recommended 3-4 times. My powerhead has one of those CO2 attachements so it wouldn't be a problem of connecting it up the reactor.

The only thing I am a bit worried about is the low KH of 2 I have in my tank. That's the way it comes out of the tap and it's good discus water. Have a look at the discus section of the forum. Thomas from Luxemburg has a nice planted discus tank and he uses CO2 as well. I'm not sure if I want to go down this road since I want to avoid a pH crash

hehe.......well I see the boys are getting quite excited by the CO2 reactor

Climbingperch you could also try using a powerhead with the CO2 line attached, some of them come with an air line attachment feature, you hook up the CO2 line and the powerhead impellor should break up the bubbles into a mist and blow them around the tank, if you own a powerhead you could try this, don't know if I would go out and buy one specifically though, but it would probably work a lot better than what you are doing now.

The heating cable won't do anything for you im afraid.

I actually have a spare powerhead at the mo, just checked it and it does have a airline hole def gonna give that a try.So all that stuff i read bout heating cables warming the roots and making plants grow faster with convection currents is bull? Suppose u can't believe everything u read in books. Thanks for all your help zig!

I get the principle. I run my 600l tank with what is trmed and HMF filter, essentially a filtermat with a powerhead behind it. Works very well, no maintenance to talk about and is dirt cheap to built. Mine cost about 35€. If you are not sure what I am talking about, google 'Hamburger Mattenfilter' and get it translated by Altavista or any such software. Turnover is 1200l per hour so only twice the volume of the tank and not the recommended 3-4 times. My powerhead has one of those CO2 attachements so it wouldn't be a problem of connecting it up the reactor.

The only thing I am a bit worried about is the low KH of 2 I have in my tank. That's the way it comes out of the tap and it's good discus water. Have a look at the discus section of the forum. Thomas from Luxemburg has a nice planted discus tank and he uses CO2 as well. I'm not sure if I want to go down this road since I want to avoid a pH crash

Sorry Holger only getting back to this now, things got busy for a while.

Holger you could try attaching the CO2 line directly to the powerhead and see how it goes, although 600l is a large tank (about 160G ?) normally people would use a CO2 reactor like the one I posted earlier, albeit maybe a scaled up version, 2 inch pipe on a dedicated filter, something like a eheim 2028 would do nicely.

The filter setup you have is interesting but 2x flow would not be enough to power a reactor of this type, the flow/reactor size really determines the CO2 dissolution rate, if the flow is to low going through the reactor it will airlock very quickly and not dissolve the CO2 efficiently at all, the more flow the more CO2 will get dissolved, normally people would probably use something like 2x eheim 2028s for a planted tank this size for filtration and use inline reactors.

A Kh of 2 will not be a problem, you will be injecting moderate amounts of CO2 somewhere in the 10-15ppm range would be good with moderate lighting perhaps 1WPG, remember WPG gidelines for large tanks are different than normal sized 20-90 gallon tanks. For instance 2WPG would be considered highlight for a tank this size.

Tomas is running around 1WPG on his tank but you will notice in the pictures he has a lot of floating plants also, this wil reduce his light to a large degree and it gives him more leeway, this is probably why he does not have to fertilise this tank so much, this puzzled me a little until I noted this.

A KH of 2 is not so important, we focus more on the GH of your water in planted tanks, GH3 or above is good, below this can lead to problems longterm, currently I have 2 tanks running one with KH0 (due to the substrate I am using) and the other with KH2, neither tanks have problems with 25ppm CO2 injection, GH is 3 in both.

Your main problem will be getting the CO2 diffused efficiently and then pushing it around the tank with so little flow IMO.

Hi Zig,
thanks for the lengthy reply. I think the issue in my tank isn't the CO2 but rather the substrate or more to the point the lack of nutrients therein.

I added some clay balls the size of a bean to the roots of my Echinodorus and the new leaves look much better.

Holger